#include <fstream>
#include <cstdio>

using namespace std;
//ifstream fin("fractii.in");
ofstream fout("fractii.out");

int x[1000100];

unsigned long long s;
int i,n,j;

int main()
{

    freopen("fractii.in","r",stdin);

    scanf("%d",&n);

 //   fin>>n;

    s+=1;

    for(i=2;i<=n;i++)
    {
        if(x[i]==0)
        {
            x[i]=i-1;
            s+=x[i];
            for(j=i*2;j<=n;j+=i)
            {
                if(x[j]==0)
                {
                    x[j]=j/i*(i-1);
                }
                else
                {
                    s-=x[j];
                    x[j]=x[j]/i*(i-1);
                }
                s+=x[j];
            }
        }
    }

    s*=2;
    s--;
    fout<<s;
    return 0;
}