#include <iostream>
#include <string>
#include <cstdio>

using namespace std;


int main()
{
    int n;

    while(cin >> n)
    {
        int *pole = new int[n];
        for(int i = 0; i < n; i++)
        {
            cin >> pole[i];
        }
        int pocetKroku = 0;

        if(n <= 3)
            cout << "OK" << endl;
        else if(pole[2] > pole[0])
        {
            for(int i = 2; i < n; i++)
            {
                if(pole[i] <= pole[i - 2])
                {
                    cout << i + 1 << endl;
                    break;
                }
                if(i == n - 1)
                    cout << "OK" << endl;
            }
        }
        else if(pole[2] < pole[0])
        {
            for(int i = 2; i < n; i++)
            {
                if(pole[i] >= pole[i - 2])
                {
                    cout << i << endl;
                    break;
                }
                if(i == n - 1)
                    cout << "OK" << endl;
            }
        }
        else cout << 3 << endl;

    }

    return 0;
}