#include<fstream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int n,i,j,v[1000001];
long s;
int numarare(int n)
{for(i=2;i<n;i++)v[i]=i-1;
for(i=2;i<=n/2;i++)
	for(j=i+i;j<=n;j+=i)v[j]-=v[i];
for(i=2;i<=n;i++)s+=2*v[i];
return s;
}
int main()
{f>>n;
g<<numarare(n);
return 0;
}