import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author cteam084
 */
class Self {

    public static enum Dir {

        NORTH, WEST, SOUTH, EAST;
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

        int numberOfInstruction = 0;
        int field[];
        do {
            String line = br.readLine();
            numberOfInstruction = Integer.parseInt(line);
            field = new int[numberOfInstruction];
            String[] ins = br.readLine().split(" ");

            for (int i = 0; i < ins.length; i++) {
                field[i] = Integer.parseInt(ins[i]);
            }
            List<Position> list = new ArrayList<Position>();

            Dir dir = Dir.NORTH;
            Position p = new Position(0, 0);
            list.add(p);

            int count = 0;
            boolean end = false;
            for (int i = 0; i < field.length; i++) {
                int moves = field[i];
                for (int j = 0; j < moves; j++) {
                    Position pos = move(dir, p);
                    

                    p = pos;
                    if (list.contains(pos)) {
                        bw.write((i) + "\n");
                        end = true;
                        break;
                    } else {
                        if (i == field.length - 1) {
                            bw.write("OK\n");
                            break;
                        }
                    }
                    list.add(pos);
                }
                if(end)
                    break;


                dir = changeDir(dir);
            }



        } while (br.ready());


        bw.flush();

    }

    public static Dir changeDir(Dir d) {
        switch (d) {
            case NORTH:
                return Dir.EAST;
            case EAST:
                return Dir.SOUTH;
            case SOUTH:
                return Dir.WEST;
            case WEST:
                return Dir.NORTH;
        }
        return null;
    }

    public static Position move(Dir d, Position p) {
        switch (d) {
            case NORTH:
                return new Position(p.x, p.y + 1);
            case EAST:
                return new Position(p.x + 1, p.y);
            case SOUTH:
                return new Position(p.x, p.y - 1);
            case WEST:
                return new Position(p.x - 1, p.y);
        }

        return null;
    }
//    public static boolean contain(List<Position> list)
//    {
//        for (int i = 0; i < list.size(); i++) {
//            for (int j = 0; j < list.size(); j++) {
//                if(i == j)
//                    continue;
//                else
//                {
//                    if(list.get(i).equals(list.get(j)))
//                        return true;
//                }
//            }
//        }
//        return false;
//    }
}

class Position {

    public int x, y;

    public Position(int x, int y) {
        this.x = x;
        this.y = y;
    }

    @Override
    public boolean equals(Object obj) {
        Position p = (Position) obj;
        return this.x == p.x && this.y == p.y;

    }
}