#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define REP(i, N) for(int i=0;i<(N);++i)
#define FOR(i, a, b) for(int i=(a);i<=(b);++i)
#define FORI(i, a, b) for(int i=(a);i<(b);++i)
#define FORD(i, a, b) for(int i=(b)-1;i>=(a);--i)

int N;
void solve(){
	int i = 0;
	if (N <= 3) {
		int pppp;
		printf("OK\n");
		for (; i < N;) {
			scanf("%d", &pppp);
			i++;
		}
		return;
	}
	int us[N];
	scanf("%d", &us[0]);
	scanf("%d", &us[1]);
	i+=2;
	
	for (; i < N;) {
		scanf("%d", &us[i]);
		i++;
		if (us[i-1] > us[i - 3]) {
			
		}
		else { break; }
	}
	if (i == N) { printf("OK\n"); return;}
	
	int omezeni;
	
	if (i <= 4 || us[i-1] < us[i - 3] - us[i - 5]) {
		omezeni = us[i-2];
	}
	else {
		omezeni = us[i-2] - us[i-4];
	}	
	int no = 0;
	for (; i < N;) {
		scanf("%d", &us[i]);
		i++;		
		if (us[i - 1] >= omezeni) {
			no = 1;
			break;
		}		
		omezeni = us[i - 3];
	}
	if (i == N && !no) {
		printf("OK\n");
	}
	else {
		printf("%d\n", i-1);
	}

	for (; i < N;) {
		int p;
		scanf("%d", &p);
		i++;
	}	
}

int main(){
	while(scanf("%d",&N)>0){
		solve();
	}
	
	return 0;
}