#include <iostream>
using namespace std; 
 
int main(){
   int i,s = 0,n;
   cin>>n;
   for(i = 1;i <= n;i++){
      s = s + i;
   }
    
   cout<<s<<endl;
   return 0;
}

/**************************************************************
	Problem: 1002
	User: zhuangsongyu
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/