#include <iostream>
#include <cmath>
#include <cstdlib>
using namespace std;
int anadr_typos(int);
int main()
{
	int n;
	cin>>n;
	cout<<anadr_typos(n);
	
	system("PAUSE");
    return 0;
}
int anadr_typos(int n)
{
	int sum;
	if (n==0) 
	{
	    sum=0;
	}else
	{
		sum=anadr_typos(n-1)+n;
	}
	return sum;
}
//Pws to skefthkame?//
//Ó=n+(n-1)+(n-2)+...+2+1+0//
//a_t(0)=0//
//a_t(1)=1=0+1=a_t(0)+1//
//a_t(2)=3=1+2=a_t(1)+2//
//a_t(3)=6=3+3=a_t(2)+3//
//a_t(4)=10=6+4=a_t(3)+4//
//kai paei legontas...//