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<a.length;i++){
              arr[i] = new Integer(a[i]);
          }
          return arr;
      }
      
      boolean run() throws Exception{
          boolean ok = true;
          
          cs.clear();
          String line = br.readLine();          
          if(line == null) 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<arr.length && ok;i++){
              len = arr[i];
              int dir = i % 4;
              
              if (!move(dir,len)){
                  System.out.println(i);
                  ok = false;
              }
          }
          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);                  
          }
      }
      
      class Coords implements Comparable<Object>{
          int x;
          int y;

        public Coords(int x, int y) {
            this.x = x;
            this.y = y;
        }
        
        void incUp(){
            this.y++;
        }
        
        void incDown(){
            this.y--;
        }
        
        void incRight(){
            this.x++;
        }
        
        void incLeft(){
            this.x--;
        }

        @Override
        public int compareTo(Object ob) {
            Coords o = (Coords)ob;
            if(this.x == o.x && this.y == o.y){
                return 0;
            }
            return 1;
        }
        
          @Override
        public String toString(){
            return "[" + x +", " + y + "]";
        }
      }
}