#include <bits/stdc++.h>

using namespace std;

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

const int NMax = 1e5 + 5;

int v[NMax];
int last[NMax];

int main(){
    int n, m, x, a, b;
    fin >> n >> m;
    for(int i = 1; i <= n; i++){
        fin >> v[i];
        if(last[v[i]] != 0){
            v[last[v[i]]] = i - last[v[i]];
        }
        last[v[i]] = i;
        v[i] = 0;
    }
    while(m--){
        fin >> a >> b;
        x = -1;
        for(int i = a; i < b; i++){
            if(v[i] != 0 && i + v[i] <= b){
                x = max(x, v[i]);
            }
        }
        fout << x << "\n";
    }
    return 0;
}