import java.io.{BufferedOutputStream, BufferedReader, InputStreamReader, PrintWriter}
import java.lang

import scala.annotation.tailrec
import scala.collection.mutable
import scala.collection.mutable.ArrayBuffer
import scala.reflect.ClassTag

object Main {
  def get[T: ClassTag](implicit in: BufferedReader, converter: String => T): T = {
    converter(in.readLine)
  }

  def getArray[T: ClassTag](implicit in: BufferedReader, converter: String => T): Array[T] = {
    get[String].split("\\s+").map[T](converter)
  }

  implicit val idConverter: String => String = s => s
  implicit val intConverter: String => Int = s => Integer.parseInt(s)
  implicit val longConverter: String => Long = s => lang.Long.parseLong(s)

  def get[T1, T2](
                   implicit in: BufferedReader,
                   converter1: String => T1,
                   converter2: String => T2
                 ): (T1, T2) = {
    getArray[String] match {
      case Array(v1, v2) => (converter1(v1), converter2(v2))
    }
  }

  def get[T1, T2, T3](
                       implicit in: BufferedReader,
                       converter1: String => T1,
                       converter2: String => T2,
                       converter3: String => T3
                     ): (T1, T2, T3) = {
    getArray[String] match {
      case Array(v1, v2, v3) => (converter1(v1), converter2(v2), converter3(v3))
    }
  }

  def get[T1, T2, T3, T4](
                           implicit in: BufferedReader,
                           converter1: String => T1,
                           converter2: String => T2,
                           converter3: String => T3,
                           converter4: String => T4
                         ): (T1, T2, T3, T4) = {
    getArray[String] match {
      case Array(v1, v2, v3, v4) => (converter1(v1), converter2(v2), converter3(v3), converter4(v4))
    }
  }

  implicit class TimesInt(val n: Int) {
    def times(f: Int => Unit): Unit = {
      for (i <- 0 until n) {
        f(i)
      }
    }
  }

  def primes(n: Long): ArrayBuffer[Long] = {
    val buf = ArrayBuffer.empty[Long]
    val s = Math.sqrt(n).toInt

    var v = n
    for (i <- 2 to s) {
      if (v == 1 || v == 0) {
        return buf
      } else {
        while (v % i == 0) {
          buf.append(i)
          v /= i
        }
      }
    }
    if (v > s) {
      buf.append(v)
    }
    buf
  }

  def divisors(n: Int): ArrayBuffer[Int] = {
    val buf = ArrayBuffer.empty[Int]
    val s = Math.sqrt(n).toInt

    for (i <- 1 to s) {
      if (n % i == 0) {
        buf.append(i)
        if (i != n / i) {
          buf.append(n / i)
        }
      }
    }
    buf
  }

  @tailrec
  def gcd(a: Long, b: Long): Long = {
    val reminder = a % b
    if (reminder == 0) {
      b
    } else {
      gcd(b, reminder)
    }
  }

  @tailrec
  def gcd(a: Int, b: Int): Int = {
    val reminder = a % b
    if (reminder == 0) {
      b
    } else {
      gcd(b, reminder)
    }
  }

  def lcm(a: Long, b: Long): Long = {
    a / gcd(a, b) * b
  }

  def toBitArray(n: Int, width: Int): Array[Boolean] = {
    val buf = ArrayBuffer.fill(width)(false)

    @tailrec
    def inner(n: Int, i: Int): Array[Boolean] = {
      buf(i) = (n & 1) == 0
      if (i == 0) {
        buf.toArray
      } else {
        inner(n / 2, i - 1)
      }
    }

    inner(n, width - 1)
  }

  def modpow(n: Long, p: Long, m: Long): Long = {
    @tailrec
    def inner(n: Long, p: Long, acc: Long): Long = {
      if (p == 0) {
        acc
      } else if ((p & 1) == 0) {
        inner(n * n % m, p >> 1, acc)
      } else {
        inner(n * n % m, p >> 1, acc * n % m)
      }
    }

    inner(n % m, p, 1)
  }

  def main(args: Array[String]): Unit = {
    implicit val in: BufferedReader = new BufferedReader(new InputStreamReader(System.in))
    val out = new PrintWriter(new BufferedOutputStream(System.out))
    val (h, w) = get[Int, Int]

    val WALL = -1
    val EMPTY = -2

    var emptyCount = 0

    val smap = Array.fill(h) {
      get[String].toCharArray.map {
        case '.' =>
          emptyCount += 1
          EMPTY
        case '#' =>
          WALL
      }
    }

    val queue = mutable.Queue.empty[(Int, Int)]
    queue.enqueue((0, 0))
    smap(0)(0) = 0

    while (queue.nonEmpty) {
      val (y, x) = queue.dequeue()
      val step = smap(y)(x) + 1

      if (x > 0 && smap(y)(x - 1) == EMPTY) {
        smap(y)(x - 1) = step
        queue.enqueue((y, x - 1))
      }
      if(y > 0 && smap(y - 1)(x) == EMPTY) {
        smap(y - 1)(x) = step
        queue.enqueue((y - 1, x))
      }
      if(x < w - 1 && smap(y)(x + 1) == EMPTY) {
        smap(y)(x + 1) = step
        queue.enqueue((y, x + 1))
      }
      if(y < h - 1 && smap(y + 1)(x) == EMPTY) {
        smap(y + 1)(x) = step
        queue.enqueue((y + 1, x))
      }
    }

    out.println(
      if (smap(h - 1)(w - 1) == EMPTY) {
        -1
      } else {
        emptyCount - smap(h - 1)(w - 1) - 1
      }
    )


    out.flush()
  }
}

Measured memory_bytes: 57300