#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)




int B[9];
//-----------------------------------------------------------------
int main() {
	rep(i, 0, 9) cin >> B[i];

	rep(i, 0, 10) if (B[i] != i + 1) {
		printf("%d\n", i + 1);
		return 0;
	}
}