#include #include using namespace std; #define NMAX 1000005 int n; int main () { // freopen("a.in","r",stdin); // freopen("a.out","w",stdout); scanf("%d",&n); if(n == 1) printf("3\n"); else if(n == 2) printf("6\n"); else { printf("%lld\n", ((long long)n - 1) / 2 * 6 + ((long long)n - 2) / 2 * 3 + 6); } return 0; }