#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <cstring>
#include <queue>
#include <stack>
#include <functional>
#include <math.h>
#include <iomanip>
using namespace std;
#define Would
#define you
const int INF = 999999999;
const int MOD = 1e9 + 7;

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