#include <stdlib.h>
#include <stdio.h>
void phi(int *phi,long n)
{
for (int i=1;i<=n;i++) phi[i]=i;

for (int i=2;i<=n;i++)
   if (phi[i]==i)
      for (int j=i;j<=n;j+=i) phi[j] /=i, phi[j] *= (i-1);
}

int main()
{
    long n,sum;
    int *v;
    freopen("fractii.in", "rt", stdin);
    freopen("fractii.out", "wt", stdout);

    scanf("%lu", &n);
    sum = 1;
    v = (int *)malloc(n*sizeof(int));
    phi(v,n);
    for(int i=2;i<=n;i++)
        sum += v[i] *2;
    printf("%lu", sum);
    return 0;
}