#include<bits/stdc++.h>
using namespace std;
int n,w;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++)
	w+=i; 
	cout<<"w="<<w;
	return 0;
}
/**************************************************************
	Problem: 1002
	User: zkl
	Language: C++
	Result: Wrong Answer
****************************************************************/