Rabbits

#include <iostream>
#include <string>
#include <vector>
using namespace std;

int compare(string a, string b) {
    if (a.length() < b.length()) return -1;
    if (a.length() > b.length()) return 1;
    return a.compare(b);
}

string fib(int n) {
    if (n <= 0) return "0";
    if (n == 1) return "1";
    
    string a = "0", b = "1";
    for (int i = 2; i <= n; i++) {
        string sum = "";
        int carry = 0;
        int j = a.length() - 1;
        int k = b.length() - 1;
        
        while (k >= 0 || j >= 0 || carry) {
            int x = j >= 0 ? a[j] - '0' : 0;
            int y = k >= 0 ? b[k] - '0' : 0;
            int current = x + y + carry;
            carry = current / 10;
            sum = char(current % 10 + '0') + sum;
            j--; k--;
        }
        
        a = b;
        b = sum;
    }
    return b;
}

int main() {
    string a, b;
    cin >> a >> b;
    
    int count = 0;
    int month = 1;
    string current;
    
    while (true) {
        current = fib(month);
        if (compare(current, b) > 0) break;
        
        if (compare(current, a) >= 0 && compare(current, b) <= 0) {
            count++;
        }
        month++;
    }
    
    cout << count << endl;
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED