#include<bits/stdc++.h>
using namespace std;
int n,ans;
void f(int s){
	ans+=s;
	if(s==1){
		return; 
	}else{
		f(s-1);
	}	
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		f(i);
	} 
	cout<<ans;
	return 0;
}


/**************************************************************
	Problem: 1148
	User: zzz
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/