【よくわかる】ABC280 C問題

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

int main() {
    string s, t;
    cin >> s >> t;
    
    int n = s.size();

    for (int i = 0; i < n; i++) {
        if (s[i] != t[i]) {
            cout << i + 1 << endl;
            return 0;
        }
    }

    cout << n + 1 << endl;
    return 0;
}