#include <bits/stdc++.h>
#define lsb(x) x & -x

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

const int NMAX = 1000005;
int a[NMAX];

int main() {
    int n;
    in >> n;
    long long sol = 1;
    for(int i = 2; i <= n; i ++)
        a[i] = i;
    for(int i = 2; i <= n; i ++) {
        if(a[i] == i) {
            for(int j = i; j <= n; j += i)
                a[j] = a[j] * (i - 1) / i;
        }
        sol += (2LL * a[i]);
    }
    out << sol;
    return 0;
}