#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i=1,j=0;
	cin>>n;
	while(i<=n){
		j=i+j;
		i++;
	} 
	cout<<j;
}
/**************************************************************
	Problem: 1002
	User: linzihang
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/