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