Undirected unweighted graph is given. Find the shortest path between two vertices of even length.
The first line contains four integers: number of vertices n, number of edges m (n,m≤105), source s and destination d (1≤s,d≤n). Each of the next m lines contains two integers a and b describing an undirected edge (a,b).
Print the shortest distance from s to d. The length of the path (number of edges in the path) must be even. If there is no path of even length between s and d, print −1.