#include <iostream>
#include <vector>

using namespace std;

int main()
{
	int N;
	vector<int> a;
	
	cin >> N;
	int res = N;
	for (int i = 0, x, left; i < N; ++i) {
		cin >> x;
		a.push_back(x);
		
		if (i == 0) left = x;
		else if (x == left + 1) ++left, --res;
		else left = x, res = N;
	}
	
	cout << res << endl;
	
	return 0;
}