import java.io.*;
import java.util.*;

public class Self {
  public static void main(String args[]) throws Exception {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String line;
    while((line = in.readLine()) != null) {
	int N = Integer.parseInt(line);

	int[] p = new int[N];
	boolean decreasing = false;
	boolean ok = true;

	line = in.readLine();
	String[] st = line.split(" ");
	
	for(int i = 0; i < N; i++){
		p[i] = Integer.parseInt(st[i]);
		if(i > 1){
		if(decreasing){
			if(p[i] >= p[i-2]){
				System.out.println((int)(i+1));	
				ok = false;
				break;
			}	
		}else{
			if(p[i] <= p[i-2]){
				decreasing = true;
				if(i > 2){
					p[i-1] -= p[i];	
					if(p[i-1] <= 0){
						System.out.println((int)(i+1));	
						ok = false;
						break;				
					}			
				}
			}
		
		
		}
		}	

	}

	if(ok){
		System.out.println("OK");	
	}

	
    }
  }
}