#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <ctype.h>

using namespace std;



struct Dvojice
{
	int a;
	int b;
	int id;
	int chybne;
};

struct Dvojice d[1000100];
long long int ids[1000100];

int compare (const void *a, const void *b)
{
	struct Dvojice a1 = *(struct Dvojice*)a;
	struct Dvojice b1 = *(struct Dvojice*)b;
	if (a1.a == b1.a)
		return (a1.b-b1.b);
	else
		return (a1.a-b1.a);
}

int compare2 (const void *a, const void *b)
{
	struct Dvojice a1 = *(struct Dvojice*)a;
	struct Dvojice b1 = *(struct Dvojice*)b;
	return (a1.id-b1.id);
}


int main(void) {
	int m, q;
	int x, y;
	int from, to, to2, od, od2, od3, pocet, ok, zac = 1;
	long long tmp;
	int i, ii;
	
	map<int, int> mapa;
	
	
	
	while (1) {
		scanf("%d %d", &m, &q);
		if (m == 0 && q == 0)
			break;
		else if (zac == 0) {
			printf("\n");
		}
		if (zac == 1)
			zac--;
		for(i=0; i < m; i++)
		{
			scanf("%lld", &tmp);
			ids[i] = tmp;
		}
	
		for(i=0; i < q; i++)
		{
			scanf("%d %d", &x, &y);
			d[i].a = x;
			d[i].b = y;
			d[i].id = i;
		}

		qsort (d, q, sizeof(struct Dvojice), compare);
		/*for (i = 0; i < q; i++)
			printf("%d %d %d\n", d[i].a, d[i].b, d[i].id);*/
		pocet = 0;
		for (i = 0; i < q; i++) {
			if (i == 0) {
				od = d[i].a-1;
				to = d[i].b-1;
				od2 = od;
				to2 = to;
				od3 = od;
			} else {
				od = d[i].a-1;
				to = d[i].b-1;
				for (ii = od2; ii < od; ii++) {
					mapa[ids[ii]]--;
					if (mapa[ids[ii]] == 1) {
						pocet--;
					}
				}
				for (ii = to+1; ii <= to2; ii++) {
					mapa[ids[ii]]--;
					if (mapa[ids[ii]] == 1)
						pocet--;
				}
				od3 = to2+1;
				to2 = to;
				od2 = od;
			}
			ok = 0;
			for (ii = od3; ii <= to; ii++) {
				mapa[ids[ii]]++;
				if (mapa[ids[ii]] == 2) {
					d[i].chybne = ids[ii];
					ok = 1;
					pocet++;
				}
			}
			if (ok == 0 && pocet > 0) {
				for (map<int, int>::iterator huh=mapa.begin(); huh!=mapa.end(); huh++) {
					if (huh->second > 1) {
						d[i].chybne = huh->first;
						break;
					}
				}
				
			} else if (ok == 0)
				d[i].chybne = -1;
		}
		qsort (d, q, sizeof(struct Dvojice), compare2);
		for (i = 0; i < q; i++) {
			if (d[i].chybne == -1)
				printf("OK\n");
			else
				printf("%d\n", d[i].chybne);
		}
		mapa.clear();
		
	}
	
	

	

	return 0;
}