#include <fstream>

using namespace std;
int v[1000007];
int n,i,k,j,x;
int main()
{   ifstream cin("fractii.in");
    ofstream cout("fractii.out");
    cin>>n;
    for(i=2; i<=n; i++)
        if(v[i]==0)
        {
            v[i]=i-1;
            for(j=2*i; j<=n; j+=i)
            {
                if(!v[j])v[j]=1;
                k=1;
                x=j/i;
                while(x%i==0)
                {
                    k*=i;;
                    x/=i;
                }
                v[j]=v[j]*(i-1)*k;
            }
        }
    long long  s=1;
    for(i=2; i<=n; i++)
       s+=2*v[i];
      //  cout<<i<<" "<<v[i]<<endl;
    cout<<s;

        return 0;
}