e156 - 1

/* e156 - 1        */
/* AC (3ms, 292KB) */
#include <cstdio>

using namespace std;

unsigned int n;

class Temp
{
    public:
        Temp(){++N; Sum += N;}

        static void Reset() {N = 0; Sum = 0;}
        static unsigned int GetSum() {return Sum;}

    private:
        static unsigned int N;
        static unsigned int Sum;
};
unsigned int Temp::N = 0;
unsigned int Temp::Sum = 0;

unsigned int Sum_Solution(unsigned int n)
{
    Temp::Reset();

    Temp *a = new Temp[n];
    delete []a;
    a = NULL;

    return Temp::GetSum();
}

int main()
{
    scanf("%u", &n);
    printf("%u", Sum_Solution(n));
    return 0;
}