#include<stdio.h>
int main()
{
	unsigned long long int n;
	scanf("%llu", &n);
	unsigned long long int ans;
	if (n % 2 > 0)
		ans = (n + 1) / 2 * n;
	else
		ans = n / 2 * (n + 1);
	printf("%llu\n", ans);
	return 0;
}