#include<fstream>
#include<iostream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int N,rez,i,j;
struct
{
    int d,m;
    bool verif;
}v[1000002];

int main()
{
    f>>N;
    v[1].d=1;v[1].m=1;
    for (i=2;i<=N;++i)
        v[i].d=i-1,v[i].m=1;
    rez=1;
    for (i=2;i<=N;++i)
    {
        if (v[i].verif==false)
        {
            for (j=i<<1;j<=N;j+=i)
            {
                v[j].verif=true;
                v[j].d-=v[i].m;
                v[i].m++;
            }
        }
        rez+=v[i].d*2;
    }
    //for (i=1;i<=N;++i)
     //   cout<<v[i].d<<' '<<v[i].m<<'\n';
    g<<rez;
    f.close();g.close();
    return 0;
}