#include <iostream>		//cin, cout
#include <vector>		//vector
#include <algorithm>	//sort,min,max,count
#include <string>		//string,getline, to_string
#include <cstdlib>		//abs(int)
#include <utility>		//swap, pair

using namespace std;

int main() {

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

	return 0;

}