#include <fstream>
#include <vector>
#define x first
#define y second
using namespace std;
class InputReader {
    public:
        InputReader() {}
        InputReader(const char *file_name) {
            input_file = fopen(file_name, "r");
            cursor = 0;
            fread(buffer, SIZE, 1, input_file);
        }
        inline InputReader &operator >>(int &n) {
            while(buffer[cursor] < '0' || buffer[cursor] > '9') {
                advance();
            }
            n = 0;
            while('0' <= buffer[cursor] && buffer[cursor] <= '9') {
                n = n * 10 + buffer[cursor] - '0';
                advance();
            }
            return *this;
        }
    private:
        FILE *input_file;
        static const int SIZE = 1 << 17;
        int cursor;
        char buffer[SIZE];
        inline void advance() {
            ++ cursor;
            if(cursor == SIZE) {
                cursor = 0;
                fread(buffer, SIZE, 1, input_file);
            }
        }
}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];
inline void build(int nod,int left,int right)
{
    if(left==right) AI[nod]=sol[left];
    else
    {
        int mid=(left+right)>>1;
        build(nod<<1,left,mid);
        build((nod<<1)+1,mid+1,right);
        AI[nod]=max(AI[nod<<1],AI[(nod<<1)+1]);
    }
}
inline void update (int nod, int left ,int right)
{
    if(left==right)
    {
        AI[nod]=val;
        return;
    }
    int mij=(left+right)>>1;
    if(poz<=mij) update(nod<<1,left,mij);
        else update((nod<<1)+1,mij+1,right);

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