#include <fstream>
#include <iostream>

using namespace std;

ifstream fin("fractii.in");
ofstream fout("fractii.out");

#define MAX 1000002

int a[MAX];

int main()
{
    int n;
    fin>>n;
    int i,j;
    for(i=1;i<=n;i++)
        a[i]=i;

    for(i=2;i<=n;i++)
        if(a[i]==i){
            for(j=i;j<=n;j+=i)
                a[j]=a[j]/i*(i-1);
        }
    int s=0;
    for(i=1;i<=n;i++)
        s+=a[i];
    s*=2;
    fout<<s<<endl;
    fin.close();
    fout.close();
    return 0;
}