#include<fstream>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int x,i,nr;
bool ciur[1000001];
int j;
int main()
{
    fin>>x;
    for(i=2;i*i<=x;i++)
        if(!ciur[i])
            for(j=i*i;j<=x;j+=i)
                ciur[j]=true;
    nr=2*x-1;
    for(i=2;i<=x;i++)
    {
        if(!ciur[i])
            nr+=(x/i-1)*(x/i-1)+(x/i);
    }
    fout<<nr;
}