#include<iostream>
using namespace std;

int solve(int B[9], int i) {
	if (B[i - 1] != i) {
		return i;
	}
	else {
		solve(B, i + 1);
	}
}

int main() {
	int B[9];
	for (int i = 0;i < 9;i++) {
		cin >> B[i];
	}
	cout << solve(B, 1);
}