#include <bits/stdc++.h>
using namespace std;

int main()
{
    set<int> st = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    for (int i = 0; i < 9; i++)
    {
        int B;
        cin >> B;
        st.erase(B);
    }
    cout << *st.begin();
}