#include <iostream>
#include <vector>

using namespace std;

int main()
{
	int n, k, i, j;
	cin >> n >> k;

	vector<unsigned int> trees(n);

	for (i = 0; i < n; i++)
	{
		cin >> trees[i];
	}

	int max = trees[0], maxi = 0;

	for (i = 1; i < n; i++)
	{
		if (i - maxi > k)
		{
			cout << maxi + 1;
			return 0;
		}

		if (trees[i] > max)
		{
			max = trees[i];
			maxi = i;
			continue;
		}
	}
	cout << -1;
}
//10 3
//6 2 1 8 4 8 7 12 9 3