#include <cstdio>
#include <cmath>

long long SUM;
int N;
int primes[1000001];
int p[300000];
int nr_primes;

void check_primes()
{
    p[nr_primes] = 2;
    nr_primes++;

    for(int i = 4; i <= N; i+=2)
    {
        primes[i] = 1;
    }

    for(int i = 3; i <= N; i+=2)
    {
        if(primes[i] == 0)
        {
            p[nr_primes] = i;
            nr_primes++;

            for(int j = 2*i; j <= N; j+=i)
            {
                primes[j] = 1;
            }
        }
    }
}

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 euler(int x)
{
    if (x == 1)
    {
        return 1;
    }
    if (primes[x] == 0)
    {
        return x - 1;
    }
    int PRODUCT = 1;
    int current = 0;
    while(x > 1)
    {
        if (x % p[current] == 0)
        {
            int count = 0;
            int total = 1;
            while (x % p[current] == 0)
            {
                total *= p[current];
                x /= p[current];
                count++;
            }
            //PRODUCT = PRODUCT * (p[current] - 1) * pow(p[current], count - 1);
            PRODUCT = PRODUCT * (p[current] - 1) * (total / p[current]);
        }
        current++;
    }
    return PRODUCT;
}

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

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

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

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