#include <stdio.h>
#include <stdlib.h>

#define MAXN 2000000

int a[MAXN];

int main()
{
	int n;
	while(scanf("%d", &n) > 0)
	{
		for(int i = 0; i < n; i++)
		{
			scanf("%d", a + i);
		}
		
		int i, pruser = 0;
		for(i = 0; i < n; i++)
		{
			if(i < 2)
			{
				continue;
			}
			
			if(a[i] <= a[i - 2])
			{
				break;
			}
		}
		
		pruser = (i >= 4) && (a[i] + a[i - 4] >= a[i - 2]);
		
		if((i == 3) && (a[i] == a[i - 2]))
		{
			pruser = 1;
		}
		
		for(i++; i < n; i++)
		{
			if(pruser)
			{
				if(a[i] + a[i - 4] >= a[i - 2])
				{
					goto FAIL;
				}
				
				pruser = 0;
			}
			
			if(a[i] >= a[i - 2])
			{
				goto FAIL;
			}
		}
		
		printf("OK\n");
		goto NEXT_INPUT;
		
		FAIL:
		printf("%d\n", i);
		
		NEXT_INPUT:;
	}
	
	return 0;
}