#include <fstream>
#include <vector>
using namespace std;
ifstream f("pq.in");
ofstream g("pq.out");
int n,t,i,j,maxim,val,poz,y,x,a,b,nr,v[1<<17],T[1<<17],sol[1<<17],AI[1<<19];
struct pt
{
    int x;
    int y;
};
vector <pt> V[1<<17];
void update (int nod, int left ,int right)
{
    if(left==right)
    {
        AI[nod]=val;
        return;
    }
    int mij=(left+right)/2;
    if(poz<=mij) update(2*nod,left,mij);
        else update(2*nod+1,mij+1,right);

    AI[nod]=max(AI[2*nod],AI[2*nod+1]);
}
void query(int nod,int left,int right)
{
    if(a<=left&&right<=b)
    {
        maxim=max(AI[nod],maxim);
        return;
    }
    int mij=(left+right)/2;
    if(a<=mij) query(2*nod,left,mij);
    if(b>mij) query(2*nod+1,mij+1,right);
}
int main()
{
    f>>n>>t;
    for(i=1;i<=n;++i)
    {
        f>>x;
        if(v[x])
        {
            poz=i;
            val=i-v[x];
            update(1,1,n);
            T[v[x]]=i;
        }
        v[x]=i;
    }
    for(i=1;i<=t;++i)
    {
        f>>x>>y;
        V[x].push_back({y,i});
    }
    val=0;
    for(i=1;i<=n;++i)
    {
        a=i;
        for(j=0;j<V[i].size();++j)
        {
            maxim=0;
            b=V[i][j].x;
            query(1,1,n);
            if(!maxim) maxim=-1;
            sol[V[i][j].y]=maxim;
        }
        poz=T[i];
        update(1,1,n);
    }
    for(i=1;i<=t;++i) g<<sol[i]<<'\n';
    return 0;
}