Minimum Number of Frogs Croaking

Given a string formed by interleaving multiple "croak" sequences, determine the minimum number of frogs that must be croaking concurrently to produce it (or return -1 if the letters violate the required "c"→"r"→"o"→"a"→"k" order). The core challenge is tracking overlapping progress through the five ordered states and reporting the maximum number active at once.