#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,a=0;
	cin>>n;
	while(n>0){
	a=a+n;
	n=n-1;
	}
	cout<<a;
	return 0;
}
/**************************************************************
	Problem: 1002
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/