// No.481 1から10
// https://yukicoder.me/problems/no/481
//

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

using namespace std;
int solve(vector<int> &written);


int main() {
    const int WRITTEN_NUMBER = 9;
    vector<int> written(WRITTEN_NUMBER);
    for (auto i = 0; i < WRITTEN_NUMBER; i++)
        cin >> written[i];

    int ans = solve(written);
    cout << ans << endl;
}

int solve(vector<int> &written) {
    vector<int> e = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    vector<int> res;
    sort(written.begin(), written.end());
    set_difference(e.begin(), e.end(), written.begin(), written.end(), inserter(res, res.end())); // e - writtenの差集合を求める
    return res[0];
}