import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.TreeSet;

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author durec4
 */
public class SIP {
    
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    
      TreeSet<Integer> cs = new TreeSet<Integer>();
      Integer actPos;
      
      public static void main(String[] args) throws Exception{
      
          SIP s = new SIP();
          while(s.run()){}          
      }
      
      int getInt(String s) throws Exception{
          return new Integer(s);
      }
      
      int[] getInts(int cnt, String[] a){
          int[] arr = new int[cnt];
          for(int i = 0;i<cnt;i++){
              arr[i] = new Integer(a[i]);
          }
          return arr;
      }
      
      boolean run() throws Exception{
          boolean ok = true;
          
          cs.clear();
          String line = br.readLine();          
          if(line.length() == 0) return false;
          int cnt = getInt(line);          
          actPos = new Integer(0);
          
          int[] arr = new int[cnt];          
          arr = getInts(cnt, br.readLine().split(" "));
          
          int len = 0;
        
          for(int i = 0;i<cnt;i++){
              len = arr[i];
              int dir = i % 4;
              
              if (!move(dir,len)){
                  System.out.println(i);
                  ok = false;
                  break;
              }
              
          }
          if (ok)
            System.out.println("OK");   
          
          return true;
      }
      
      boolean do_moveRight(int steps){
          for(int i=0;i<steps;i++){              
              actPos += 1;
              
              if (!cs.add(actPos)){
                return false;
              }
          }
          return true;
      }
      
      boolean do_moveLeft(int steps){
          for(int i=0;i<steps;i++){
//              actPos = new Coords(actPos.x, actPos.y);
              actPos -=1;
              if (!cs.add(actPos)){
                  return false;
              };
          }
          return true; 
      }
      
      boolean do_moveDown(int steps){
          for(int i=0;i<steps;i++){
//              actPos = new Coords(actPos.x, actPos.y);
              actPos -=10;
              if (!cs.add(actPos)){
                  return false;
              };
          }
          return true;
      }
      
      boolean do_moveUp(int steps){
          for(int i=0;i<steps;i++){
//              actPos = new Coords(actPos.x, actPos.y);
              actPos += 10;
              if (!cs.add(actPos)){
                  return false;
              };
          }
          return true;
      }
      
      boolean move(int dir, int steps){
          switch(dir){
              case 0:
                  return do_moveUp(steps);
              case 1:
                  return do_moveRight(steps);
              case 2:
                  return do_moveDown(steps);
              default:
                  return do_moveLeft(steps);                  
          }
      }
      
     
}