Undirected unweighted graph is given. Find the shortest path between two vertices of even length. \InputFile The first line contains four integers: number of vertices $n$, number of edges $m~(n, m \le 10^5)$, source $s$ and destination $d~(1 \le s, d \le n)$. Each of the next $m$ lines contains two integers $a$ and $b$ describing an undirected edge $(a, b)$. \OutputFile 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 $-1$. \includegraphics{https://static.e-olymp.com/content/6a/6adee2ac9b12616702d7346fe468c745baa3b60c.gif}