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





/**************************************************************
	Problem: 1002
	User: 078899
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/