시저 암호

def solution(s, n):
    ret = ''
    for i in s:
        if i.isupper():
            ret += chr((ord(i) - ord('A') + n)%26 + ord('A'))
        elif i.islower():
            ret += chr((ord(i) - ord('a') + n)%26 + ord('a'))
        else:
            ret += i
    return ret