#include <bits/stdc++.h> 
using namespace std;
int main() {
    int a,n;
    cin>>n;
    a=(1+n)*n/2;
    cout<<a; 
} 
/**************************************************************
	Problem: 1002
	User: chenmingyu
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/