#include <bits/stdc++.h>
#define rep(i, n) for (ll i = 0; i < n; ++i)
typedef long long ll;
using namespace std;
const int INF = 1e9;

int main() {
    int a[9];
    rep(i, 9) cin >> a[i];

    rep(i, 9) {
        if (a[i] != i + 1) {
            cout << i + 1 << endl;
            return 0;
        }
    }

    cout << 10 << endl;

    return 0;
}