The Recipe Tree

You are organizing a cooking contest. A complex dish is made by combining raw ingredients and intermediate products. Given the steps, find the longest sequence of transformations required to reach a final dish. Every item has at most one parent (the item it is used to create). Input: The first line contains N, the number of items. The next N-1 lines contain two strings: 'A B', meaning ingredient A is used to create product B. One item is the final dish (it is not used to create anything). Output: The integer length of the longest chain of ingredients leading to the final dish (number of items in the chain). Example: Input: 4 Flour Dough Dough Bread Wheat Flour Output: 4