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

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