#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;
using P = pair<int, int>;
using namespace std;

bool ok[11];
int main() {
    rep(i, 9) {
        int tmp;
        cin >> tmp;
        ok[tmp] = true;
    }

    for (int i=1; i<=10; ++i) {
        if (!ok[i]) {
            cout << i << endl;
            return 0;
        }
    }
}