#include <fstream>

using namespace std;
int prim(int i)
{
    int d;
    for(d=2;d<i;d++)
        if(i%d!=0) return 1;
    return 0;

}

int main()
{
    ifstream in("fractii.in");
    ofstream out("fractii.out");
    int n,i,j,nr=0;
    in>>n;
    nr=n;
    j=2;
    for(i=2;i<=n;i++)
    {
        if(prim(i)==1)
            nr=nr+i-1;
        else
            nr=nr+2;


    }
    out<<nr;
    in.close();
    out.close();
    return 0;
}