Exam Solution:

#include <bits/stdc++.h>

using namespace std;

int main(){

    // #ifndef TESTING
    // freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
    // #endif
    int friendCorrect;
    int friendWrong;
    string myAns;
    string friendAns;
    cin >> friendCorrect;
    cin >> myAns;
    cin >> friendAns;
    friendWrong = friendAns.length() - friendCorrect;

    int myMaxCorrect = 0;
    for(int i = 0; i < myAns.length(); i++){
        if (myAns[i] == friendAns[i] && friendCorrect){
            friendCorrect--;
            myMaxCorrect++;
        }
        else if(myAns[i] != friendAns[i] && friendWrong){
            friendWrong--;
            myMaxCorrect++;
        }
    }
    cout << myMaxCorrect;
    
    return 0;
}