#include<bits/stdc++.h> 
using namespace std;
int main()
{
    int n;
    cin>>n;
    cout<<(1+n)*n/2;
}
/**************************************************************
	Problem: 2100
	User: yangjunwen
	Language: C++
	Result: Accepted
	Time:37 ms
	Memory:2072 kb
****************************************************************/