#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin >> n ;
    cout << n * (n + 1)/2;
    return 0;
 
}
/**************************************************************
	Problem: 1002
	User: liyunshuo
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/