POJ.2413 How many Fibs?

1.Problem
http://poj.org/problem?id=2413

2.Idea
Enumerating first 500 fibs numbers.

3.Source

 string add(string a, string b)  
 {  
      if (a == "") return b;  
      if (b == "") return a;  
      if (a.length() < b.length()) swap(a, b);  
      int d = a.length() - b.length();  
      for (int i = 0; i < d; i++) {  
           b = "0" + b;  
      }  
      int car = 0;  
      int n = a.length();  
      for (int i = n - 1; i >= 0; i--) {  
           int tmp = car + a[i] + b[i] - '0' - '0';  
           a[i] = '0' + (tmp % 10);  
           car = tmp / 10;  
      }  
      if (car > 0) return "1" + a;  
      else return a;  
 }  
 bool isNotSmaller(string a, string b) // a <= b -> true  
 {  
      if (a == b) return true;  
      if (a.length() < b.length()) return true;  
      if (a.length() == b.length() && a <= b) return true;  
      return false;  
 }  
 bool isNotGreater(string a, string b) // a >= b -> true  
 {  
      if (a == b) return true;  
      if (a.length() > b.length()) return true;  
      if (a.length() == b.length() && a >= b) return true;  
      return false;  
 }  
 vector<string> fibs;  
 int main()  
 {  
      fibs.push_back("1");  
      fibs.push_back("1");  
      for (int i = 2; i < 500; i++) {  
           string tmp = add(fibs[i - 1], fibs[i - 2]);  
           fibs.push_back(tmp);  
      }  
      while (true) {  
           string a, b;  
           cin >> a >> b;  
           if (a == "0" && b == "0") break;  
           int cnt = 0;  
           for (int i = 1; i < 500; i++) {  
                if (isNotSmaller(a, fibs[i]) && isNotGreater(b, fibs[i])) cnt++;  
           }  
           cout << cnt << endl;  
      }  
      return 0;  
 }