import java.util.Scanner;
public class a17 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("输入一个数");
int n = sc.nextInt();
int Sn;
int an = n;
Sn = (1+an)*n/2; //a1 = 1
System.out.println(Sn);
}
}