如果使用整型來儲存結果，會導致結果錯誤。

import java.util.Scanner;

public class Main{
	public static void main(String[] args) {
		//執行超時
		/*Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		double s = 0;
		if (n<=10000) {
			for (int i=1;i<=n;i++) {
				s = s + i;
			}
		} else {
			s = 50005000;
			for (int i=1000;i<n;i++) {
				s = s+i;
			}
		}
		
		System.out.println(String.format("%.0f", s));
	}*/
		Scanner scanner = new Scanner(System.in);
		long n = scanner.nextLong();
		long s = (1+n)*n/2;
		System.out.println(s);
	}
}