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