#include <stdio.h>

int main(void)
{
  long kroky, i;
  long polekrokov[1000001];
  short boo;

  while (scanf("%ld", &kroky) == 1)
    {
      
	  for (i = 0; i < kroky; i++)
	    scanf("%ld", &polekrokov[i]);
	  if (kroky <= 3)
	printf("OK\n");
      else
	{

	  boo = 1;
	  
	  for (i = 0; i < kroky-2; i++)
	    {
	  
	      if (polekrokov[i] >= polekrokov[i+2])
		{
		  printf("%ld\n", i+3);
		  boo = 0;
		  break;
		}
	      
	    }
	  
	  if (boo == 1)
	    printf("OK\n");
	}

    }

      return 0;

}