技術標籤：資料結構與演算法

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Test {

    public static void main(String[] args) {
        System.out.print("輸入：");
        Scanner s = new Scanner(System.in)
 
;
        int n = s.nextInt();
        System.out.print( "輸出："+ sum(n));
    }


    public static int sum(int n) {
            return (int) (Math.pow(n, 2) + n) >> 1;
    }
}