import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
while(true) {
int num = sc.nextInt();
if (num == 0) break;
//(1)
System.out.println(pyramids(num));
//(2)
}
}
private static int pyramids(int num) {
int result = 0;
for (int i = 1; i <= num; i++) {
result += i;
//(3)
}
return result;
//(4)
}
}