You are given a string croakOfFrogs made of characters 'c','r','o','a','k' only. Multiple frogs can croak simultaneously, but each frog must output "croak" in order. Return the minimum number of frogs needed, or -1 if it's impossible.

Example 1:

Input: croakcroak
Output: 1

Example 2:

Input: crcoakroak
Output: 2

Input format: A single string.

Output format: Minimum frogs or -1.