#include <fstream>

using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int i,p,n,a[1000005],s,k;
int main()
{
    fin>>n;
    for(i=2;i<=n;i++)
    {
        if(a[i]==0)
        {
        a[i]=a[i]+i-1;
        p=1;
        k=0;
        while(p<=n/i)
        {
            a[i*p]-=k;
            k++;
            p++;
        }
        }
        else
            a[i]=a[i]+i-1;
    }
    s=1;
    for(i=2;i<=n;i++)
        s+=2*a[i];
    fout<<s;
    return 0;
}