#include <cstdio>
#include <map>
using namespace std;

const int U = 1<<20;

map<int,int> ma;
int c[2*U];

int pyt(int a, int b, int x = 0, int y = U-1, int v = 1) {
    if(a <= x && y <= b)
        return c[v];
    int s = (x+y) / 2;
    int ret = -10;
    if(a <= s)
        ret = max(ret, pyt(a,b, x,s,v+v));
    if(b > s)
        ret = max(ret, pyt(a,b, s+1,y,v+v+1));
    return ret;
}

int a[U-13];
int main() {
    int n,q;
    while(scanf("%d %d",&n,&q) == 2 && n) {
        ma.clear();
        for(int i = 0; i < n; i++) {
            scanf("%d",&a[i]);
            c[i+U] = -1;
            if(ma.count(a[i]))
                c[i+U] = ma[a[i]];
            ma[a[i]] = i;
        }
        for(int i = U-1; i>=1; i--) c[i] = max(c[i+i], c[i+i+1]);
        while(q--) {
            int aa,b;
            scanf("%d %d",&aa,&b);
            int w = pyt(aa-1, b-1);
            if(w < aa-1) puts("OK");
            else printf("%d\n", a[w]);
        }
        puts("");
    }
    return 0;
}