#include<bits/stdc++.h>
using namespace std;
int main(){
	int i=1,h=0,a;
	cin>>a;
	while(i<=a){
		h=h+i;
		i++;
	
	}
	cout<<h;

}
/**************************************************************
	Problem: 1002
	User: huanglingkai
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/