#include<bits/stdc++.h>
using namespace std;
int main() {
    int i,n;
    cin>>n;
    i=(n+1)*n/2;
    cout<<i; 
}
/**************************************************************
	Problem: 1002
	User: 12345678
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2072 kb
****************************************************************/