#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <set>
#include <algorithm>

using namespace std;

//#define debug(fmt, ...) fprintf(stderr, fmt, ## __VA_ARGS__)
#define debug(fmt, ...) 
#define OFFS 1048576
#define INF 1000000000

static pair<int, int> Tree[2*OFFS];
static int Arr[OFFS], Next[OFFS];

static void compute(int v, int p, int q)
{
	if(q-p == 1) {
		Tree[v] = make_pair(Next[p], Arr[p]);
		return;
	}

	int m = (p+q)/2;
	compute(2*v, p, m);
	compute(2*v+1, m, q);

    Tree[v] = min(Tree[2*v], Tree[2*v+1]);
}

static pair<int, int> query(int v, int p, int q, int a, int b)
{
	if(p == a && q == b)
		return Tree[v];

	int m = (p+q)/2;
	if(b <= m) return query(2*v,   p,m, a,b);
	if(a >= m) return query(2*v+1, m,q, a,b);
	return min(query(2*v, p,m, a,m), query(2*v+1, m,q, m,b));
}

static void solve()
{
	int n, q;
	scanf("%d %d",&n,&q);
	if(!n && !q) exit(0);
	for(int i=0; i<n; i++)
        scanf("%d", &Arr[i]);

    for(int i=0; i<n; i++)
        Next[i] = INF;

    {
        set<pair<int, int> > S;
        for(int i=0; i<n; i++) {
            set<pair<int, int> >::iterator it = S.lower_bound(make_pair(Arr[i], -1));
            if(it != S.end() && it->first == Arr[i]) {
                Next[it->second] = i;
                S.erase(it);
            }
            S.insert(make_pair(Arr[i], i));
        }
    }

	compute(1, 0, OFFS);

	while(q--) {
		int a,b;
		scanf("%d %d",&a,&b);
        pair<int, int> ans = query(1, 0,OFFS, a-1,b);
        if(ans.first < b)
            printf("%d\n", ans.second);
        else
            printf("OK\n");
	}
	printf("\n");
}

int main(void) {
	for(;;) solve();
}