#include <fstream>

using namespace std;


ifstream in("fractii.in");
ofstream out("fractii.out");

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

int main()
{
    cin>>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+=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;
}