#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int n, k;
    cin >> n >> k;
    vector <int> mfa (n + 1);
    for (int i = 1; i <= n; i++)
    {
        cin >> mfa[i];
    }
    int hatar;
    int i = 1, j;
    while (i <= n)
    {
        hatar = (n < i + k ? n : i + k);
        j = i + 1;
        while (j <= hatar && mfa[i] >= mfa [j])
        {
            j++;
        }
        if (j > hatar)
        {
            cout << i;
            return 0;
        }
        i = j;
    }
    cout << - 1;
    return 0;
}