#include <cstdio>
using namespace std;
unsigned long long sol;
int n,i,v[1000000],j;
int main()
{
freopen("fractii.in","r",stdin);
freopen("fractii.out","w",stdout);
scanf("%d",&n);
for (i=1;i<=n;i++) v[i]=i-1;
for (i=2;i<=n;i++)
for (j=i+i;j<=n;j+=i)
v[j]-=v[i];
for (i=2;i<=n;i++) sol+=v[i];
sol*=2;rez++;
printf("%ld",sol);
}