What the help!

#include <iostream>
#include <string>
using namespace std;
int main(){
    double rate;
    cin >> rate;
    string s1, s2;
    cin >> s1 >> s2;
    int len = s1.length();
    int sum = 0;
    for(int i = 0; i < len; i++){
        if(s1[i] == s2[i]){
            sum++;
        }
    }
    if(sum * 1.0 / len >= rate){
        cout << "yes";
    }else{
        cout << "no";
    }
    return 0;
}