package sprint6.tasks.F

import java.io.BufferedReader
import java.io.InputStreamReader
import java.util.*

typealias Edges = Map<Int, List<Int>>

fun main() {
    val buffer = BufferedReader(InputStreamReader(System.`in`))
    val edges = readGraph(buffer, true)
    buffer.readLine().split(" ").map { it.toInt() }
        .let { println(edges.bfs(it[0], it[1])) }

}

fun readGraph(buffer: BufferedReader, notOriented: Boolean = false): Edges {
    val (vertexCount, edgeCount) = buffer.readLine().split(" ").map { it.toInt() }
    val edgesLocal = List(vertexCount) { it + 1 }.associateWith { mutableListOf<Int>() }

    repeat(edgeCount) {
        val (vertex, toVertex) = buffer.readLine().split(" ").map { it.toInt() }
        edgesLocal[vertex]!!.add(toVertex)
        if (notOriented)
            edgesLocal[toVertex]!!.add(vertex)
    }

    return edgesLocal
}

enum class Color {
    WHITE,
    GREY,
    BLACK
}

fun Edges.bfs(v: Int, u: Int): String {
    val colors = Array(size + 1) { Color.WHITE }
    val distance = IntArray(size + 1) { -1 }
    val queue = LinkedList<Int>()
    queue.push(v)
    distance[v] = 0
    colors[v] = Color.GREY
    while (queue.any() && distance[u] < 0) {
        val cur = queue.poll()
        this[cur]!!.forEach {
            if (colors[it] == Color.WHITE) {
                distance[it] = distance[cur] + 1
                queue.add(it)
                colors[it] = Color.GREY
            }
        }
        colors[cur] = Color.BLACK
    }
    return distance[u].toString()
}