#include <cstdio>

using namespace std;

int main ()
{
    int n;
    scanf ("%d", &n);

    if (n == 1)
    {
        printf ("3\n");
        return 0;
    }

    long long sum = 3LL;
    --n;

    sum += 3LL * (1LL * (n + 1) / 2LL);
    sum += 6LL * (1LL * n / 2LL);

    printf ("%lld\n", sum);

    return 0;
}