#include <iostream>
using namespace std;

void solve(){
    int n = 1;
    while(n <= 9){
        int input;
        cin >> input;
        if(n != input) {
            cout << n << endl; 
            return;
        }
        n++;
    }
    cout << 10 << endl;
}

int main() {
    int t = 1;
    // cin >> t;

    while(t--){
        solve();
    }

    return 0;
}