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

namespace Problem4_FirstLargerThanNeighbours
{
    class FirstLargerThanNeighbours
    {
        static void Main()
        {
            int[] inputNums = Console.ReadLine().Split(' ').Select(p => int.Parse(p)).ToArray();
            Console.WriteLine(GetIndexOfFirstElementLargerThanNeighbours(inputNums));

        }
        static int GetIndexOfFirstElementLargerThanNeighbours(int[] numbers)
        {
            int index = 0;
            bool isBigger = false;
            for (int i = 0; i <= numbers.Length - 1; i++)
            {
                index = i;
                isBigger = false;

                if (i == numbers.Length - 1)
                {
                    isBigger = (numbers[i] > numbers[i - 1]);

                    break;

                }
                if (i == 0 && numbers[i] > numbers[i + 1])
                {

                    isBigger = true;

                    break;
                }

                if (numbers[i] > numbers[i + 1] && numbers[i] > numbers[i - 1])
                {
                    isBigger = true;

                    break;
                }

            }
            int n = 0;
            if(isBigger)
            {
                n = index;
            }
            else
            {
                n = -1;
            }
            return n;

        }
    }
}