#include<bits/stdc++.h>
using namespace std;
int main() {
	int i,n;
	cin>>n;
	i=(n+1)*n/2;
	cout<<i; 
}

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