#include <cstdio>
#include <cmath>

int N, SUM;

int pow(int x, int y)
{
    if (y == 0)
    {
        return 1;
    }
    if (y == 1)
    {
        return x;
    }
    if (y % 2 == 0)
    {
        return pow(x, y / 2) * pow(x, y / 2);
    }
    return pow(x, y / 2) * pow(x, y / 2) * x;
}

int prime(int x)
{
    if (x % 2 == 0)
    {
        return 0;
    }
    for(int i = 3; i <= sqrt(x); i += 2)
    {
        if (x % i == 0)
        {
            return 0;
        }
    }
    return 1;
}

int euler(int x)
{
    if (x == 1)
    {
        return 1;
    }
    if (prime(x) == 1)
    {
        return x - 1;
    }
    int PRODUCT = 1;
    int current = 2;
    while(x > 1)
    {
        if (x % current == 0)
        {
            int count = 0;
            while (x % current == 0)
            {
                x /= current;
                count++;
            }
            PRODUCT = PRODUCT * (current - 1) * pow(current, count - 1);
        }
        current++;
    }
    return PRODUCT;
}

int main()
{
    freopen("fractii.in", "r", stdin);
    freopen("fractii.out", "w", stdout);
    scanf("%d", &N);

    SUM = 1; // FOR CASE: 1 / 1

    for (int i = 2; i <= N; i++)
    {
        SUM += 2 * euler(i);
        //printf("%d\n", i);
    }

    printf("%d\n", SUM);
    return 0;
}