#include <stdio.h>
#include <malloc.h>
/// <summary>
/// 入力された数字を返す
/// </summary>
/// <returns></returns>
int ReadNum() {
	char c = getchar();
	int num = 0;
	int numCnt = 0;
	while (c != '\n') {
		num = num * 10 + c - '0';
		c = getchar();
	}
	return num;
}
int sum(int n) {
	int sum = 0;
	for (int i = 1;i <= n;i++) {
		sum += i;
	}
	return sum;
}

int main()
{
	printf("%d\n", sum(ReadNum()));
}