#include <bits/stdc++.h>

using namespace std;

int main()
{
bool a[10] = {};
for (int i = 0; i < 9; ++i) { int tmp; cin >> tmp; a[tmp - 1] = true; }
for (int i = 0; i < 10; ++i) if (!a[i]) { cout << i + 1 << endl; return 0; }
}