#include <fstream>
#include <algorithm>
#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')&&buffer[cursor]!='-') {
                advance();
            }
            n =0;
            semn= 1;
            if(buffer[cursor]=='-') semn=-1,advance();
            while('0' <= buffer[cursor] && buffer[cursor] <= '9') {
                n = n * 10 + buffer[cursor] - '0';
                advance();
            }
            n*=semn;
            return *this;
        }
    private:
        FILE *input_file;
        static const int SIZE = 1 << 17;
        int cursor,semn;
        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,step,xi,a,b,nr,v[1<<17];
pair <int,int> V[1<<17];
struct cmp
{
    bool operator () (pair <int,int> a,pair <int,int> b)
    {
        return a.y-a.x<b.y-b.x;
    }
};
int main()
{
    f>>n>>t;
    for(i=1;i<=n;++i)
    {
        f>>xi;
        if(v[xi]) V[++nr]={v[xi],i};
        v[xi]=i;
    }
    sort(V+1,V+nr+1,cmp());
    while(t--)
    {
        f>>a>>b;
        for(i=0,step=1<<16;step;step>>=1)
            if(i+step<=nr&&V[i+step].y-V[i+step].x<=b-a) i+=step;
        if(!i) g<<"-1\n";
        while(i)
        {
            if(V[i].x>=a&&V[i].y<=b)
            {
                g<<V[i].y-V[i].x<<'\n';
                break;
            }
            --i;
            if(!i) g<<"-1\n";
        }
    }
    return 0;
}