#include <cstdio>
#include <vector>
#include <map>
#include <algorithm>

using namespace std;

pair<int, int> get(int begin, int end, int st, int ee, int x, vector<pair<int, int> >&data) {
	if (ee <= begin) return make_pair(100000000, -1);
	if (st >= end) return   make_pair(100000000, -1);
	if (st >= begin && ee <= end) return data[x];
	return min(get(begin, end, st, (st+ee)/2, 2*x, data),
			   get(begin, end, (st+ee)/2, ee, 2*x+1, data));
}

void ss(int x, vector<pair<int, int> >&data) {
	data[x] = min(data[2*x], data[2*x+1]);
	if (x != 1)
		ss(x/2, data);
}

void go(int m, int q) {
	vector<int> nums(m);
	for (int i = 0; i < m; i++)
		scanf("%d", &nums[i]);
	vector<int> closest(m);
	map<int, int> last;
	vector<int> clo2(m, -1);
	for (int i = 0; i < m; i++) {
		if (last.count(nums[i])==0) {
			closest[i] = 1000000000;
		} else {
			closest[i] = i - last[nums[i]];
			clo2[last[nums[i]]] = i;
		}
		last[nums[i]] = i;
	}
	vector<pair<int, int> > data(2097152);
	int pos = 1048576;
	for (int i = 0; i < m; i++) {
		data[i+pos] = make_pair(closest[i], i+1);
	}
	for (int i = pos-1; i > 0; i--) {
		data[i] = min(data[2*i], data[2*i+1]);
	}
	vector<pair<pair<int, int>, int> > Q(q);
	for (int i = 0; i < q; i++) {
		scanf("%d %d", &Q[i].first.first, &Q[i].first.second);
		Q[i].first.first--;
		Q[i].second = i;
	}
	sort(Q.begin(), Q.end());
	vector<int> out(q, -1);
	int ll = 0;
	for (int i = 0; i < q; i++) {
		for (int j = ll; j < Q[i].first.first; j++) {
			if (clo2[j] == -1) continue;
			data[clo2[j]+pos].first = 1000000000;
			ss((clo2[j]+pos)/2, data);
		}
		ll = Q[i].first.first;
		int b = Q[i].first.first;
		int e = Q[i].first.second;
		pair<int, int> gg = get(b, e, 0, pos, 1, data);
/*		printf("%d %d %d\n", gg.first, gg.second, e-b);
		if (gg.first < e-b) {
			printf("%d\n", gg.second);	
		} else {
			printf("OK\n");
		}*/
		if (gg.first < e-b) {
			out[Q[i].second] = gg.second;
		}
	}
	for (int i = 0; i < q; i++) {
		if (out[i] == -1)
			printf("OK\n");
		else
			printf("%d\n", out[i]);
	}
	printf("\n");
}

int main() {
	while(true) {
		int m, q; scanf("%d %d", &m, &q);
		if (m == 0 && q == 0) break;
		go(m, q);
	}
}