Submission #4

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s, t;
    cin >> s >> t;
    int answer = 0;
    for(int i = 0; i < s.size(); ++i) {
        if(s[i] != t[i]) ++answer;
    }
    cout << answer << endl;
    return 0;
}