#include <cstdio>
#include <map>

using namespace std;

int m[1000001];
int volt[1000001];
int mes, q, i;
int a, f;
long long x;
bool ok;

int main() {
	map<int, int>::iterator it;
	map<int, int> mp;
	for (i = 0; i < 1000001; ++i) volt[i] = -1;
	x = 0;
	while (1){
		f = 0;
		mp.clear();
		scanf("%d %d", &mes, &q);
		if (mes == 0) break;
		for (i = 1; i <= mes; i++) {
			scanf("%d", &a);
			it = mp.find(a);
			if (it == mp.end()) {
				m[i] = f;
				mp[a] = f++;
			} else {
				m[i] = mp[a];
			}
		}
		for (int j = 0; j < q; j++){
			scanf("%d %d", &a, &f);
			ok = true;
			for (i = a; i <= f; i++){
				if (volt[m[i]] == x){
					printf("%d\n", i);
					ok = false;
					break;
				} else {
					volt[m[i]] = x;
				}
			}
			++x;
			if (ok) printf("OK\n");
		}
		scanf("\n");
		printf("\n");
	}

	return 0;
}