import java.util.*;

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

/**
 *
 * @author cteam24
 */
public class unique {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        for(;;) {
            int size = s.nextInt();
            int qs = s.nextInt();
            if( size == 0 && qs == 0 ) {
                break;
            }
            int[] k = new int[size];
            for( int i = 0; i < size; i++ ) {
                k[i] = s.nextInt();
            }
            for( int j = 0; j < qs; j++ ) {
                Set<Integer> set = new HashSet<Integer>();
                int from = s.nextInt() - 1;
                int to = s.nextInt() - 1;
                boolean first = true;
                for( int i = from; i <= to; i++ ) {
                    int n = k[i];
                    if( set.contains( n ) ) {
                        System.out.println( n );
                        first = false;
                        break;
                    }
                    set.add( n );
                }
                if( first )
                    System.out.println("OK");
            }
        }
    }

}