UVA 10079 Pizza Cutting Solution

import java.util.Scanner;

class Main {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc = new Scanner(System.in);
while (sc.hasNext()) {
long no = sc.nextLong();
if (no<0l) break;
System.out.println(1+((no*(no+1l))/2l));

}
}

}