#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <numeric>

using namespace std;
typedef long long int lint;

int main()
{
	int a = 0, b, i;
	for (i = 1; i <= 9; i++) {
		cin >> b;
		if (b - a == 2) {
			cout << b - 1 << endl;
			break;
		}
		a = b;
	}
	if(i == 10)
		cout << 10 << endl;

	return 0;
}