#include <bits/stdc++.h>
#define maxN 100002
#define zeros(x) x & (-x)
using namespace std;
int n, q, occ[maxN], p[maxN], aib[maxN], ans[maxN];
struct query
{
    int l, r, pq;
}v[maxN];
int cmp(const query a, const query b)
{
    return a.r < b.r;
}
void read()
{
    int i, x;
    freopen("pq.in", "r", stdin);
    scanf("%d %d", &n, &q);
    for (i = 1; i <= n; ++ i)
    {
        scanf("%d", &x);
        if (occ[x])
            p[i] = occ[x];

        occ[x] = i;
    }
    for (i = 1; i <= q; ++ i)
        {
            scanf("%d %d", &v[i].l, &v[i].r);
            v[i].pq = i;
        }
}
void Update(int x, int y)
{
    int i;
    for (i = x; i > 0; i -= zeros(i))
        if (aib[i] < y)
           aib[i] = y;
}
int Query(int x)
{
    int i, ans = 0;
    for (i = x; i <= n; i += zeros(i))
        if (aib[i] > ans)
           ans = aib[i];
    return ans;
}
void solve()
{
    int i, j = 1;
    sort(v + 1, v + q + 1, cmp);
    for (i = 1; i <= q; ++ i)
     {
         while (j <= v[i].r)
         {
             if (p[j])
             Update(p[j], j - p[j]);
             ++ j;
         }
         ans[v[i].pq] = Query(v[i].l);
     }
}
void write()
{
    int i;
    freopen("pq.out", "w", stdout);
    for (i = 1; i <= q; ++ i)
        {
            if (ans[i] == 0)
                ans[i] = -1;
            printf("%d\n", ans[i]);
        }
}
int main()
{
    read();
    solve();
    write();
    return 0;
}