water

#include<iostream>
using namespace std;
int main(){
	int n;
	long long a[60];
	cin >> n;
	a[1] = 1;
	a[2] = 4;
	for(int i = 3;i <= n;i++){
		a[i] = a[i-1] + i;
	}
	cout << a[n];
	return 0;
}