Code is open source, be sure to give credit to Connor Godinich and I

A simple 2 step cipher I made with a partner for Computer Science 1. 

import time
input("Please make your window at least this big, then press enter ------------------------------------------------------------------------------------->")
print('''  _    _           _     _                         _____           _ _       _      _       ______                             _   _             
 | |  | |         | |   | |               ___     / ____|         | (_)     (_)    | |     |  ____|                           | | (_)            
 | |__| | __ _  __| | __| | ___  _ __    ( _ )   | |  __  ___   __| |_ _ __  _  ___| |__   | |__   _ __   ___ _ __ _   _ _ __ | |_ _  ___  _ __  
 |  __  |/ _` |/ _` |/ _` |/ _ \| '_ \   / _ \/\ | | |_ |/ _ \ / _` | | '_ \| |/ __| '_ \  |  __| | '_ \ / __| '__| | | | '_ \| __| |/ _ \| '_ \ 
 | |  | | (_| | (_| | (_| | (_) | | | | | (_>  < | |__| | (_) | (_| | | | | | | (__| | | | | |____| | | | (__| |  | |_| | |_) | |_| | (_) | | | |
 |_|  |_|\__,_|\__,_|\__,_|\___/|_| |_|  \___/\/  \_____|\___/ \__,_|_|_| |_|_|\___|_| |_| |______|_| |_|\___|_|   \__, | .__/ \__|_|\___/|_| |_|
                                                                                                                    __/ | |                      
                                                                                                                   |___/|_|                      ''')
print("Hello and welcome to the Haddon and Godinich Encryption program!")
time.sleep(2)
run = True
while run == True:
    birthyear = int(input("What is your birth year? (Make sure this is 4 digits) : "))

    orig_txt = input("Type in your message: (No Numbers or other characters) ")
    print("")

#    input("Press enter to continue")
    Stage1 = orig_txt.replace("a", "D")
    Stage1 = Stage1.replace("b", "E")
    Stage1 = Stage1.replace("c", "F")
    Stage1 = Stage1.replace("d", "G")
    Stage1 = Stage1.replace("e", "H")
    Stage1 = Stage1.replace("f", "I")
    Stage1 = Stage1.replace("g", "J")
    Stage1 = Stage1.replace("h", "K")
    Stage1 = Stage1.replace("i", "L")
    Stage1 = Stage1.replace("j", "M")
    Stage1 = Stage1.replace("k", "N")
    Stage1 = Stage1.replace("l", "O")
    Stage1 = Stage1.replace("m", "P")
    Stage1 = Stage1.replace("n", "Q")
    Stage1 = Stage1.replace("o", "R")
    Stage1 = Stage1.replace("p", "S")
    Stage1 = Stage1.replace("q", "T")
    Stage1 = Stage1.replace("r", "U")
    Stage1 = Stage1.replace("s", "V")
    Stage1 = Stage1.replace("t", "W")
    Stage1 = Stage1.replace("u", "X")
    Stage1 = Stage1.replace("v", "Y")
    Stage1 = Stage1.replace("w", "Z")
    Stage1 = Stage1.replace("x", "A")
    Stage1 = Stage1.replace("y", "B")
    Stage1 = Stage1.replace("z", "C")
    Stage1 = Stage1.replace("9", "2")
    Stage1 = Stage1.replace("8", "1")
    Stage1 = Stage1.replace("7", "0")
    Stage1 = Stage1.replace("6", "9")
    Stage1 = Stage1.replace("5", "8")
    Stage1 = Stage1.replace("4", "7")
    Stage1 = Stage1.replace("3", "6")
    Stage1 = Stage1.replace("2", "5")
    Stage1 = Stage1.replace("1", "4")
    Stage1 = Stage1.replace("0", "3")

    stage2 = ""

    for character in Stage1:
        if character == "A":
                stage2 += str( 20+birthyear )
    for character in Stage1:
        if character == "B":
                stage2 += str(16+birthyear)
    for character in Stage1:
        if character == "C":
                stage2 += str(67+birthyear)
    for character in Stage1:
        if character == "D":
                stage2 += str(26+birthyear)
    for character in Stage1:
        if character == "E":
                stage2 += str(17+birthyear)
    for character in Stage1:
        if character == "F":
                stage2 += str(44+birthyear)
    for character in Stage1:
        if character == "G":
                stage2 += str(14+birthyear)
    for character in Stage1:
        if character == "H":
                stage2 += str(19+birthyear)
    for character in Stage1:
        if character == "I":
                stage2 += str(18+birthyear)
    for character in Stage1:
        if character == "J":
                stage2 += str(11+birthyear)
    for character in Stage1:
        if character == "K":
                stage2 += str(33+birthyear)
    for character in Stage1:
        if character == "L":
                stage2 += str(83+birthyear)
    for character in Stage1:
        if character == "M":
                stage2 += str(13+birthyear)
    for character in Stage1:
        if character == "N":
                stage2 += str(12+birthyear)
    for character in Stage1:
        if character == "O":
                stage2 += str(15+birthyear)
    for character in Stage1:
        if character == "P":
                stage2 += str(95+birthyear)
    for character in Stage1:
        if character == "Q":
                stage2 += str(62+birthyear)
    for character in Stage1:
        if character == "R":
                stage2 += str(50+birthyear)
    for character in Stage1:
        if character == "T":
                stage2 += str(26+birthyear)
    for character in Stage1:
        if character == "U":
                stage2 += str(72+birthyear)
    for character in Stage1:
        if character == "V":
                stage2 += str(12+birthyear)
    for character in Stage1:
        if character == "W":
                stage2 += str(10+birthyear)
    for character in Stage1:
        if character == "X":
                stage2 += str(56+birthyear)
    for character in Stage1:
        if character == "Y":
                stage2 += str(52+birthyear)
    for character in Stage1:
        if character == "Z":
                stage2 += str(45+birthyear)
    for character in Stage1:
        if character == " ":
                stage2 += str(84+birthyear)
    print(stage2)
    print("")