#include <bits/stdc++.h>

using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
long long int n,i,s,d,p,j;
int main()
{
    fin>>n;
    s=1;
    for(i=2;i<=n;i++)
    {
        d=2;
        p=i;
        j=i;
        while(d*d<=j)
        {
            if(j%d==0)
            {
                p=(p*(d-1))/d;
                while(j%d==0)
                {
                    j=j/d;
                }
            }
            d++;
        }
        if(j>1)
        p=(p*(j-1))/j;
        s=s+p*2;
    }
    fout<<s;
}