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

int main()
{
	vector<int> b( 10 );
	for( int i = 0; i < 9; i++ ) {
		int B;
		cin >> B;
		B--;
		b[B] = 1;
	}

	int ans;
	for( int i = 0; i < 10; i++ ) {
		if( b[i] == 0 ) ans = i + 1;
	}

	cout << ans << endl;
}