How Many Fibs? 字符串转换处理

import java.util.*;
import java.io.*;
import java.lang.*;
import java.math.*;
import java.text.*;
class Main
{
    public static void main(String args[])
    {
        Scanner cin=new Scanner(System.in);
        int i,j=0,k=0,flags;
        BigInteger a,b,c[]=new BigInteger[501];
        c[0]=BigInteger.valueOf(1);
        c[1]=BigInteger.valueOf(2);
        String s1,s2;
        for(i=2;i<500;i++)
        {
            c[i]=c[i-1].add(c[i-2]);
        }
        while(cin.hasNext())
        {
            flags=0;
            s1=cin.next();
            s2=cin.next();
            a=new BigInteger(s1);
            b=new BigInteger(s2);
            if(b.compareTo(BigInteger.valueOf(0))==0)break;
            for(i=0;i<500;i++)
            {
                if(flags==0)
                {
                    if(c[i].compareTo(a)>=0)
                    {
                        j=i;
                        flags=1;
                    }
                }
                if(c[i].compareTo(b)==1)
                {
                    k=i;
                    break;
                }
            }
            System.out.println(k-j);
        }
    }
}