#include <stdio.h>
#include <stdlib.h>

int sum(int a_number);

int main(void) {
	int a_number = 0;
	scanf("%d", &a_number);
	printf("%d\n", sum(a_number));
}

int sum(int a_number) {
	int result = 0;
	for (int i = 1; i <= a_number; i++) {
		result += i;
	}
	return result;
}