随机数发红包会报异常

import java.util.Scanner;
import java.util.Random;
public class a{	
public static void main(String[] args){
	System.out.println("抢红包");
	System.out.println("请输入红包金额");
	Scanner in=new Scanner(System.in);
	double total=in.nextDouble();
	System.out.println("请输入红包个数");
	int num=in.nextInt();
	double min=0.01;
	while(total/num<min){
		System.out.println("输入的金额太小不够分请重新输入红包金额");
		total=in.nextDouble();
		System.out.println("请输入红包个数");	
		num=in.nextInt();
	}
	if(total/num==min){
		for(int i=1;i<=num;i++){
		System.out.println("第"+i+"个红包是0.01元");
				
	}
	}
	else
	{Random x=new Random();
	
	for(int i=1;i<num;i++ ){
		if(total/num==min){
		System.out.println("第"+i+"个红包是0.01元");
		total=total-0.01;	
		continue;	
	}
	
		
		double max=total-(num-i)*min;
		double b=max-min;
		double now=(double)x.nextInt((int)(b*100))/100;
		double money=now+min;
		System.out.println("第"+i+"次红包是 "+String.format("%.2f",money)+"元");
		total=total-money;
	}
	System.out.println("第"+num+"次红包是 "+String.format("%.2f",total)+"元");
	in.close();
	}
 }
}
	

Exception in thread "main" java.lang.IllegalArgumentException: bound must be pos
itive
        at java.util.Random.nextInt(Random.java:388)
        at a.main(a.java:37)

 当输入1元金额，红包个数为99或98的时候会报异常请大神指点一下原因是什么

double max=total-(num-i)*min;  这里为负数了
double b=max-min;     这里为负数了
然后x.nextInt（）里面传入的书得大于0，不然会抛出java.lang.IllegalArgumentException异常