藍橋杯 矩陣翻硬币

題目連結：​​矩陣翻硬币​​

import java.io.*;
import java.math.BigInteger;
import java.util.Scanner;

public class Main {
    static BigInteger cal(BigInteger ans) {
        BigInteger l,r,res = BigInteger.ZERO;
        l = BigInteger.ONE;r = ans;
        while(l.compareTo(r) != 1) {
            BigInteger mid = (l.add(r)).divide(BigInteger.valueOf(2));
            if((mid.multiply(mid)).compareTo(ans) == -1) {
                res = mid;
                l = mid.add(BigInteger.ONE);
            }
            else {
                r = mid.subtract(BigInteger.ONE);
            }
        }
        return res;
    }
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        BigInteger n,m,ans;
        n = cin.nextBigInteger();
        m = cin.nextBigInteger();
        n = cal(n);m = cal(m);
        ans = n.multiply(m);
        System.out.println(ans);