import java.util.Scanner;

public class Task15 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.print("Please enter n: ");
		int n = sc.nextInt();
		int sum = 0;
		int i = 1;
		do {
			sum += i;
			i++;
		}while(i <= n);
		System.out.println("sum = " + sum);
	}

}