import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int n = scan.nextInt();
Sum sum = new Sum();
sum.sumz(n);
}
}
class Sum {
public void sumz(int n) {
long sum = 0;
for(int i = n; i >= 1; i--) {
sum += i;
}
System.out.println(sum);
}
}