#include <algorithm>
#include <cstdio>
#include <map>
#include <vector>
using namespace std;
int main() {
	int m, q, b, e, M[1000001];
	bool first = true;
	while (true) {
		scanf("%d %d", &m, &q);
		if (m == 0 && q == 0) break;
		if (!first) puts("");
		else first = false;
		map<int, vector<int> > keys;
		for (int i = 1; i <= m; i++) {
			scanf("%d", M + i);
			keys[M[i]].push_back(i);
		}
		#if 0
		for (map<int, vector<int> >::iterator i = keys.begin(); i != keys.end(); i++) {
			printf("%d: ", i->first);
			for (vector<int>::iterator j = i->second.begin(); j != i->second.end(); j++) {
				printf("%d ", *j);
			}
			puts("");
		}
		#endif
		for (int i = 0; i < q; i++) {
			scanf("%d %d", &b, &e);
			vector<int>::iterator itb, ite;
			int bad = -1;
			for (int i = b; i <= e; i++) {
				vector<int> c = keys[M[i]];
				itb = lower_bound(c.begin(), c.end(), b);
				ite = upper_bound(c.begin(), c.end(), e);
				int count = int(ite - itb);
				if (count > 1) {
					bad = M[i];
					break;
				}
			}
			if (bad == -1) puts("OK");
			else printf("%d\n", bad);
		}
	}
	return 0;
}