#include <iostream>
//#include <vector>
//#include <algorithm>
//#include <string>
//#include <iomanip>

using namespace std;

int main()
{
	for (int i = 1; i <= 10; i++)
	{
		int B;
		cin >> B;

		if (B != i)
		{
			cout << i << endl;
			break;
		}
	}

	return 0;
}