#include<iostream>
using namespace std;
int a[10000];
int main(){
	int n,a;
	cin>>n;
	a=0;
	while(n!=0){
		a=a+n;
		n=n-1;
	}
	cout<<a;
    return 0;
}

/**************************************************************
	Problem: 2100
	User: xuanhua
	Language: C++
	Result: Accepted
	Time:45 ms
	Memory:2112 kb
****************************************************************/