#include <iostream>
#include <fstream>

using namespace std;


int main()
{
    ifstream in("pq.in");
    ofstream out("pq.out");

    int N,Q, L, R;
    in>>N>>Q;

    int m[N][N];
    int v[N+1];

    for(int i = 1 ; i<=N; ++i)
    {
        in>>v[i];
    }

    for( int i=1; i<=N; ++i )
    {
        for( int j = i; j<=N; ++j )
        {
            if( v[i] == v[j] )
            {
                m[i][j] = 1;
            }
            else
            {
                m[i][j] = 0;
            }
        }
    }


    while( Q-- != 0 )
    {
        in>>L>>R;

        int cost = 0;
        int index = L;

        for( int i=L; i<=R; ++i )
        {
            if( m[L][i] == m[L][index] )
            {
                if( cost < (i - index) )
                {
                    cost = (i - index);
                }
                index = i;
            }
        }

        if(cost == 0)
        {
            out<<-1<<endl;
        }
        else
        {
            out<< cost<<endl;
        }

    }

    in.close();
    out.close();
    return 0;
}