프로그래머스) 문자열 겹쳐쓰

def solution(my_string, overwrite_string, s):
    my_string = list(my_string)

    for i in range(len(overwrite_string)):
        my_string[s] = overwrite_string[i]
        s += 1

    answer = ''.join(my_string)

    return answer