#include<fstream>
using namespace std;
long long phi[1000100],n,s=1;
int main() {
    int i,j;
    ifstream in("fractii.in");
    in>>n;
    in.close();
    for(i=1;i<=n;phi[i]=i,i++);
    for(i=2;i<=n;i++)
        if(phi[i]==i)
            for(j=i;j<=n+1;j+=i)
                phi[j]=phi[j]/i*(i-1);
    ofstream out("fractii.out");
    for(i=2;i<=n;s+=2*phi[i],i++);
    out<<s<<'\n';
    out.close();
    return 0;
}