TWINS C++

#include <bits/stdc++.h>
using namespace std;

int p[1000005],n,k;
void nhap()
{
    scanf("%d%d",&n,&k);
}

void sang()
{
    int j;
    p[0]=1;p[1]=1;
    for (int i=2;i<=int(sqrt(n));i++)
        if (p[i]==0)
        {
            j=i*i;
            while (j<=n)
            {
                p[j]=1;
                j+=i;
            }
        }
}

void xuli()
{
    sang();
    int res=0;
    for (int i=2;i<=n-k;i++)
        if (p[i]==0)
            if (p[i+k]==0) res++;
    printf("%d",res);
}

int main()
{
    freopen("twins.inp","r",stdin);
    freopen("twins.out","w",stdout);
    nhap();
    xuli();
}