#include<bits/stdc++.h>
using namespace std;
int main(){
	int s=1,h=0,n;
	cin>>n;
	while(s<=n){  //1 2 3 4 5 6 7 8 9 10
		h=s+h;	
		s++; 
	}
	cout<<h;
	
	return 0;
}
/**************************************************************
	Problem: 1002
	User: huanghao
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/