text = "Hey You!"
key = 3

result = ""
for symbol in text:
    if symbol>='A' and symbol<='Z':
        symbol = chr(ord(symbol)+ord('a')-ord('A'))
    if symbol>='a' and symbol<='z':
        nummer = ord(symbol)+key
        if nummer<ord('a'):
            nummer = nummer+26
        if nummer>ord('z'):
            nummer = nummer-26
        symbol = chr(nummer)
    result = result + symbol

print(result)