#define _CRT_SECURE_NO_WARNINGS
#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING
#include <bits/stdc++.h>
using namespace std;
int main()
{
    unsigned x;
    while (~scanf("%u", &x))
        printf("%u\n\n", x * (x + 1) / 2);
    return 0;
}