#include<iostream>
#include<fstream>

using namespace std;

ifstream f("fractii.in");
ofstream g("fractii.out");

int const NMax = 1000000;
int V[NMax];
int n;
long long sol;

void Solve()
{
    int i, j, k;
    f>>n;
    sol = 1;
    for(i=2; i<=n; i++){
        sol += (i - V[i] - 1) * 2;
        if(V[i] == 0)
            for(j=2*i, k=1; j<=n; j+=i, k++)
                V[j] += k;
    }

    g<<sol<<"\n";
}

int main()
{
    Solve();
    return 0;
}