Problem Statement

You are an archaeologist exploring an ancient ruin consisting of N hidden chambers (numbered 1 to N ), connected by M secret tunnels. Each tunnel allows movement between two chambers but can only be used in one direction . A treasure is known to be located in a specific chamber D , and you start your journey from a given chamber S . Your task is to determine whether you can reach the treasure and, if so, find the minimum number of steps (tunnel traversals) required to reach it from the starting chamber. If reaching the treasure is impossible, print -1 . Input Format First line: one integer N (number of chambers). Second line: one integer M (number of tunnels). Third line: one integer S (starting chamber). Fourth line: one integer D (chamber containing the treasure). Next M lines: each line contains two integers u v , representing a one-way tunnel from chamber u to chamber v . Output Format A single integer: the minimum number of tunnel traversals required to reach D from S . If no vali