#include <fstream>

using namespace std;
ifstream in("fractii.in");
ofstream out("fractii.out");

const int MAX=1000001;
int fi[MAX],n;

int main()
{   in>> n;
    for(int i=1;i<=n;i++){
        fi[i]=i;
    }
    for(int i=2;i<=n;i++){
        if(fi[i]==i){
            for(int j=i;j<=n;j=j+i){
                fi[j]=fi[j]-fi[j]/i;
            }
        }
    }

    long long ans=-1;

    for(int i=1;i<=n;i++){
        ans=ans+2*fi[i];
    }
    out<< ans;

    return 0;
}