#include <bits/stdc++.h>
using namespace std;

int main() {
	int N;
	while(cin >> N) {
		vector<int> V(N);
		for(int i =0; i < N; i++) cin >> V[i];
		bool mimo =true, ok =true;
		for(int i =2; i < N; i++) {
			if(mimo) {
				if(V[i] > V[i-2]) continue;
				mimo =false;
				int x =V[i-2];
				if(i >= 4) x -=V[i-4];
				if(i == N-1) continue;
				if(V[i] >= x && V[i-1] <= V[i+1]+((i == 2)?0:V[i-3])) {cout << i+1 << "\n"; ok =false; break;}
				if(V[i] < x && V[i-1] <= V[i+1]) {cout << i+1 << "\n"; ok =false; break;}
				i++;
				continue;}
			if(V[i-2] <= V[i]) {cout << i << "\n"; ok =false; break;}
			}
		if(ok) cout << "OK\n";}
	}