import java.io.PrintWriter
import java.util.*

fun PrintWriter.solve() {
    val n = nextInt()
    val m = nextInt()
    val adj = Array(n) { mutableListOf<Int>() }
    for (i in 0 until m) {
        val v1 = nextInt() - 1
        val v2 = nextInt() - 1
        adj[v1].add(v2)
        adj[v2].add(v1)
    }
    val que: Queue<Pair<Int, Int>> = ArrayDeque()
    val visited = BooleanArray(n) { false }
    visited[0] = true
    que.add(0 to 0)
    while (que.isNotEmpty()) {
        val (v, s) = que.poll()
        if (v == n - 1) {
            println(s)
            return
        }
        for (w in adj[v]) {
            if (!visited[w]) {
                que.add(w to s + 1)
                visited[w] = true
            }
        }
    }
    println(-1)
}

fun main() {
    val writer = PrintWriter(System.out, false)
    writer.solve()
    writer.flush()
}

// region Scanner
private var st = StringTokenizer("")
private val br = System.`in`.bufferedReader()

fun next(): String {
    while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine())
    return st.nextToken()
}

fun nextInt() = next().toInt()
fun nextLong() = next().toLong()
fun nextLine() = br.readLine()
fun nextDouble() = next().toDouble()
// endregion