#include <bits/stdc++.h>
using namespace std;
int s[400005];
long long sum[400005];
int main() {
    int i, j, n;
    scanf("%d", &n);
    memset(s, 1, sizeof(s));
    if (n == 1) {
        printf("6\n");
        return 0;
    }
    s[1] = 1;
    for (i = 2; i <= n; i++) {
        s[i] = i;
    }
    for (i = 2; i <= n; i++) {
        if (s[i] == i) {
            for (j = i; j <= n; j = j + i) {
                s[j] = s[j] / i * (i - 1);
            }
        }
    }
    sum[1] = 1;
    for (i = 2; i <= n; i++) {
        sum[i] = sum[i - 1] + s[i];
    }
    printf("%lld\n", sum[n] * 6);
}