Reachable Nodes Count

Count the number of nodes reachable from a given starting node in a directed graph. The input consists of N (the number of nodes), followed by M edges (directed pairs u, v), and finally a single integer representing the starting node. For example: 5 0 1 1 2 0 3 3 4 1 In this case, the output should be the count of nodes reachable from node 1, which is 2 (nodes 2 and 4).