#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <utility>
#include <iomanip>
using namespace std;

int main(void) {
	int x;
	for (int i = 1; i <= 10; i++) {
		cin >> x;
		if (x != i) {
			cout << i << endl;
			return 0;
		}
	}
	return 0;
}