Generations to Root

In a bureaucracy, every employee has exactly one supervisor. The top-most supervisor is always named 'ROOT'. Given a list of employee-supervisor pairs and a starting employee name, find out how many steps it takes to reach 'ROOT'. Input Format: Line 1: An integer K, the number of pairs. Next K lines: Two strings 'Employee Supervisor' separated by a space. Last line: The name of the employee to start from. Output Format: An integer representing the number of steps to reach 'ROOT'. Example: Input: 3 Alice Bob Bob Charlie Charlie ROOT Alice Output: 3