문자열 겹쳐쓰기

using System;

public class Solution {
    public string solution(string my_string, string overwrite_string, int s) {
        
        string str = my_string.Substring(0,s);
        string over_str=my_string.Substring(s+overwrite_string.Length);
        string answer = str+overwrite_string+over_str;
        return answer;
    }
}