poj 2413 How many Fibs?

#include <iostream>
#include <string>
using namespace std;
bool compare(string str1,string str2)
{
    if(str1.size()==str2.size())
        return str1>=str2;
    else
        return str1.size()>str2.size();
}
string ADD_INT(string str1, string str2)        
{
    string str;
        string::size_type l1, l2;
            int i;
            l1 = str1.size(); l2 = str2.size();
            if(l1 < l2)        
                for(i = 1; i <= l2 - l1; i++)
                    str1 = '0' + str1;
            else
                for(i = 1; i <= l1 - l2; i++)
                    str2 = '0' + str2;
            int int1 = 0, int2 = 0;        
            for(i = str1.size() - 1; i >= 0; i--)
            { 
                int1 = ( str1[i]+str2[i] -  96  + int2 ) % 10;  
                int2 = ( str1[i]+str2[i] -  96  + int2 ) / 10; 
                str = char(int1+48) + str;
            }
            if(int2 != 0) str = char(int2+48) + str;    
    return str;
}
string str[500];
void creat()
{
    str[0]="1";str[1]="2";
    for(int i=2;i<500;++i)
        str[i]=ADD_INT(str[i-1],str[i-2]);
}
int main()
{
    int i,j,dist;string a,b;
    creat();
    while(cin>>a>>b&&b!="0")
    {
        dist=0;
        for(i=0;;++i)
        {
            if(compare(str[i],a))
                break;
        }
        for(j=i;;++j)
        {
            if(compare(str[j],b))
            {
                if(str[j]==b)
                    dist++;
                break;
            }
        }
        dist+=j-i;
        cout<<dist<<endl;
    }
    return 0;
}