#include <iostream>
#include <vector>
#include <algorithm>

#define REP(i, a, b) for (int i = int(a); i < int(b); i++)

using namespace std;

typedef long long int lli;

int main() {
    int num[10] = {};
    REP (i, 0, 9) {
        int n;
        cin >> n;
        num[n - 1]++;
    }
    REP (i, 0, 10) {
        if (!num[i]) {
            cout << i + 1 << endl;
            break;
        }
    }
    return 0;
}