#include <bits/stdc++.h>
using namespace std;
#define FOR(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define FORR(i,l,n) for(int (i)=l;(i)<(int)(n);++(i))
void solve() {
	FOR(i, 9) {
		int n;
		cin >> n;
		if (n != i + 1){
			cout << i + 1;
			break;
		}
	}
}
int main() {
	ios::sync_with_stdio(false);
	solve();
	return 0;
}