public class Main { public static void main(String[] args) { Scanner s = new Scanner(System.in); int n = s.nextInt(); if (n < 0 || n > 1001){ return; } int g = 10; int o = 990; if (n > o){ System.out.println(1.000000); }else { BigDecimal k = calc(o,n); BigDecimal m = calc(1000,n); BigDecimal r = k.divide(m,BigDecimal.ROUND_HALF_UP); BigDecimal res = BigDecimal.valueOf(1).subtract(r); System.out.println(String.format("%.6f",res)); } } public static BigDecimal calc(int n, int m){ BigDecimal s = BigDecimal.valueOf(1); BigDecimal m2 = BigDecimal.valueOf(1); m = m > (n - m) ? (n - m) : m; for (int i = m; i > 0; i--){ s = s.multiply(BigDecimal.valueOf(n)); m2 = m2.multiply(BigDecimal.valueOf(i)); } return s.divide(m2,BigDecimal.ROUND_HALF_UP); } } 崩溃中。