#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <utility>
#include <stack>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <list>

#define SIZEOF(a) (sizeof(a)/sizeof(a[0]))
#define FILL(a, b) fill (a,a+SIZEOF(a),b)
#define FOR(a,b,c) for(int a=b; a<=c; a++)
#define FORARR(i,a) for(usigned i=0; i<SIZEOF(a); i++)
#define FOREACH(a,b) for(__typeof((b).begin()) a=(b).begin(); a!=(b).end(); a++)
#define GETI(a) scanf("%d", &a)

using namespace std;

struct interval {
	int begin, end, num;
	interval(int b, int e, int n) : begin(b), end(e), num(n) {}
	interval() : begin(0), end(0), num(0) {}
};

bool operator<(const interval& one, const interval& two) {
	return one.begin < two.begin;
}

enum eventType { IB, QB, QE };

struct event {
	eventType type;
	int pos;
	interval i;
	event(eventType type, int pos, interval i) : type(type), pos(pos), i(i) {}
	// pro type QB nebo QE je v i.num cislo query, jinak cislo intervalu
};

bool operator<(const event& one, const event& two) {
	return one.pos < two.pos;
}



int main(void) {

	int M, Q;
	while (scanf("%d %d", &M, &Q) == 2 && M > 0) {
		vector<event> events;
		map<int,int> positions; // num -> position in the list
		FOR(i,0,M-1) {
			// nacist klice
			int K;
			scanf("%d", &K);
			map<int,int>::iterator f = positions.find(K);
			if (f == positions.end()) {
				positions[K] = i;
			}
			else {
				events.push_back(event(IB, 2*(f->second+1)+1, interval(f->second+1, i+1, K)));
				positions[K] = i;
			}
			
		}
		FOR(j,0,Q-1) {
			// pozadavky
			int B, E;
			scanf("%d %d", &B, &E);
			events.push_back(event(QB, 2*B, interval(B, E, j)));
			events.push_back(event(QE, 2*E, interval(B, E, j)));
		}
	
		sort(events.begin(), events.end());
		
		map<int,interval> openQueries;
		vector<int> queryResults(Q, -1);
		
		FOREACH(e, events) {
//			printf("event: ");
			if (e->type == QB) {
//				printf("QB, %d, %d %d\n", e->pos, e->i.begin, e->i.end);
				openQueries[e->i.num] = e->i;
			}
			else if (e->type == QE) {
//				printf("QE, %d, %d %d\n", e->pos, e->i.begin, e->i.end);
				openQueries.erase(e->i.num);
//				queryResults[e->i.num] = -1; // neni treba
			}
			else {
				// IB
				vector<int> toDelete;
//				printf("IB, %d, %d %d %d\n", e->pos, e->i.begin, e->i.end, e->i.num);
				FOREACH(q, openQueries) {
					if (e->i.end <= q->second.end) {
						// interval padl do query
//#ifdef DEBUG
//						printf("interval %d %d num %d padol do query %d %d\n",e->i.begin, e->i.end, e->i.num, q->second.begin, q->second.end);
//#endif
						queryResults[q->second.num] = e->i.num;
						toDelete.push_back(e->i.num);
					}
				}
				FOREACH(bz,toDelete) {
					openQueries.erase(*bz);
				}
			}
		}
		
		FOR(i,0,Q-1) {
			if (queryResults[i] >= 0) {
				printf("%d\n", queryResults[i]);
			}
			else {
				printf("OK\n");
			}
		}
		printf("\n");
	}


	return 0;

}