#include<bits/stdc++.h>
using namespace std;
int main()
{int n,i=1,s=0;
cin>>n;
while(i<=n){

s=s+i;
i++;}
cout<<s;
	return 0;
}

/**************************************************************
	Problem: 1002
	User: sf751616
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/