using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace fasor1
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] s = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int n = s[0]; 
            int k = s[1]; 
            int[] magas = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int jf = magas[0];
            int ind = 1; 
            for (int i = 0; i < n-k; i++)
            {
                if (jf<magas[i])
                {
                    jf = magas[i];
                    ind = i;
                }
            }
            if (ind == 1)
            {
                ind = -1;
            }
            Console.WriteLine(ind);
            Console.ReadLine();
        }
    }
}