#include <stdio.h>
 int main()
{
	int i;
	int sum = 0;
	for (i = 1; i <= 100; i++)
	{
		sum += i;
	}
	printf ("%d\n",sum);
	return 0;
} 

 int fun1(int n)
{
	if (n == 1)
		return 1;
	int result = fun1(n-1) + n;
	return result;
}
int main()
{
	int n;
	scanf ("%d",&n);
	fun1(n);
	printf ("%d\n",fun1(n));
	return 0;
}


int main()
{
	int i = 1;
	int j;
	int sum = 0;
	scanf ("%d",&j);
	while (i < j)
	{	
		sum += i + j;
		i++;
		j--;
	}
	if (i == j)
		sum += i;
	
	printf ("%d\n",sum);
	return 0;
}