#include <bits/stdc++.h>
using namespace std;

ifstream in("pq.in");
ofstream out("pq.out");

const int N_MAX = 1e5, Q_MAX = 1e5, A_MAX = 99999;

struct Query
{
    int st, dr, ind;
    bool operator <(const Query& other) const
    {
        if(st == other.st)
            return dr < other.dr;
        return st < other.st;
    }
};

int n, m;
int a[N_MAX + 2];
Query q[Q_MAX + 2];

int ans[Q_MAX + 2], last[A_MAX + 2];
int aib[N_MAX + 2];

void update(int pos, int val)
{
    while(pos <= n)
    {
        aib[pos] = max(aib[pos], val);
        pos += pos & (-pos);
    }
}

int query(int pos)
{
    int ans = 0;
    while(pos)
    {
        ans = max(ans, aib[pos]);
        pos -= pos & (-pos);
    }

    return ans;
}

int main()
{
    in >> n >> m;
    for(int i = 1; i <= n; i++)
        in >> a[i];

    for(int i = 1; i <= m; i++)
    {
        in >> q[i].st >> q[i].dr;
        q[i].ind = i;
    }

    sort(q + 1, q + m + 1);

    int j = m;
    for(int i = n; i >= 1; i--)
    {
        if(last[a[i]])
            update(last[a[i]], last[a[i]] - i);
        last[a[i]] = i;

        while(q[j].st == i)
        {
            int val = query(q[j].dr);
            if(val == 0)
                val = -1;

            ans[q[j].ind] = val;
            j--;
        }
    }

    for(int i = 1; i <= m; i++)
        out << ans[i] << '\n';

    return 0;
}