凯撒密码

a = input("3045\n")
for i in range(len(a)):
    if ord('a')<=ord(a[i])<=ord('z'):
        b = (ord(a[i]) + 3 - ord('a')) % 26 + ord('a')
        print(chr(b),end="")
    elif ord('A')<=ord(a[i])<=ord('Z'):
        b = (ord(a[i]) + 3 - ord('A')) % 26 + ord('A')
        print(chr(b),end="")
    else:
        print(a[i],end="")