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

int main()
{
	int pocet,i,p,v = 0;
	while(scanf("%d",&pocet) == 1){
		int pole[pocet];		
		for(i=0;i<pocet;i++){
			scanf("%d",&pole[i]);
		}


		v = 0;
		p=0;
		while((p+2)<=pocet){
			if(pole[0] < pole[2]){
				if(pole[p] < pole[p]){
					v = p+1;
					p = pocet + 1;			
				}			
			}

			if(pole[0] > pole[2]){
				if(pole[0] > pole[2]){
					v = p+1;
					p = pocet +1;			
				}			
			}

			if(pole[0] == pole[2]){
				if(pole[p+1] < pole[p+3]){
					v = p+1;
					p = pocet + 1;			
				}			
			}

			p++;
		}

		if(v == 0){
			printf("OK\n");
		}
		if(v != 0){
			printf("%d\n",v);			
		}	
	}

    return 0;
}