#include <iostream.h>
#include <fstream.h>
int main()
{
    unsigned long int n,p=0;
    int c=0;
    fstream f("fractii.in",ios::in);
    fstream g("fractii.out",ios::out);
    bool prim[2000000];
    f>>n;
    for(int i=2;i<=n;i++)
    if(!prim[i])
    {
                c++;
                for(int j=2*i;j<=n;j=j+i)
                prim[j]=1;
                }
    p+=2*c-1;
    for(unsigned long int k=2;k<=n;k++)
    p+=2*c-2*k;
    g<<p;
}