#include <algorithm>
#include <array>
#include <cstdio>
#include <iostream>
#include <numeric>
#include <optional>
#include <vector>

using namespace std;

int main() {
    array<bool, 10> bs;
    for (auto i = 0; i < size(bs); ++i) {
        bs[i] = false;
    }
    for (auto i = 0; i < size(bs) - 1; ++i) {
        int32_t b;
        cin >> b;
        bs[b - 1] = true;
    }
    for (auto i = 0; i < size(bs); ++i) {
        if (!bs[i])
            cout << i + 1 << endl;
    }
    return 0;
}