#include <fstream>
#include <vector>

using namespace std;

int main() {
    //freopen("a.in", "r", stdin);
    //freopen("a.out", "w", stdout);
    int n;
    scanf("%d", &n);
    if (n == 1)
        printf("3\n");
    else {
        long long answer = 3 + 3LL * (n / 2) + 6LL * ((n - 1) / 2);
        printf("%lld\n", answer);
    }
    return 0;
}