佬，能帮我看看第一题什么问题嘛，55% ``` public class Main { public static BigDecimal calculate(int n){ if(n < 2){ return BigDecimal.ZERO; } BigDecimal num = new BigDecimal(2); BigDecimal devided = BigDecimal.valueOf(n).multiply(BigDecimal.valueOf(n - 1)); return num.divide(devided, 15, RoundingMode.HALF_UP); } public static void main(String[] args) { Scanner in = new Scanner(System.in); int count = in.nextInt(); BigDecimal property = Main.calculate(count); System.out.println(property.setScale(10, RoundingMode.HALF_DOWN)); } } ```