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




    return 0;
}

/**************************************************************
	Problem: 1002
	User: caiqiaoxi
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/