lowercase_alphabet = string.ascii_lowercase
    uppercase_alphabet = string.ascii_uppercase

    result = []
    for letter in s:
        if letter in lowercase_alphabet:
            x = lowercase_alphabet.index(letter)
            new_x = (x + k) % len(lowercase_alphabet)
            result.append(lowercase_alphabet[new_x])
        elif letter in uppercase_alphabet:
            x = uppercase_alphabet.index(letter)
            new_x = (x + k) % len(uppercase_alphabet)
            result.append(uppercase_alphabet[new_x])
        else:
            result.append(letter)

    return ''.join(result)