#include<iostream>
using namespace std;

int main()
{
	int n, i, j, a[100000], b, c;

	cin >> n;

	for (i = 1; i <= n; i++) cin >> a[i];

	for (i = n; i >= 2; i--)
	{
		for (j = 1; j <= n; j++)
		{
			if (a[j] == i - 1) b = j;
			if (a[j] == i) c = j;
		}

		if (b > c)
		{
			cout << i - 1 << endl;
			return 0;
		}
	}
	cout << 0 << endl;
}