#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define rep(i, n) for (i = 0; i < n; i++)
#define rrep(i, n) for (i = n; i >= 0; i--)
#define max(a, b) (a > b ? a : b)
#define min(a, b) (a < b ? a : b)

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

    int ans, i;
    rep(i, n + 1) ans += i;

    printf("%d\n", ans);
    return 0;
}