#include <fstream>
#define DIM 1000010


using namespace std;

int fi[DIM];
long long sol;

int n, i, j;

int main() {
    ifstream fin ("fractii.in");
    ofstream fout("fractii.out");

    fin>>n;

    for (i=1;i<=n;i++) {
        fi[i] = i;
    }

    sol = 1;
    for (i=2;i<=n;i++) {
        if (fi[i] == i)
            for (j=i;j<=n;j+=i)
                fi[j] = fi[j] / i * (i-1);
        sol += 2 * fi[i];
    }

    fout<<sol<<"\n";
    return 0;
}