#[allow(unused_imports)]
use std::char::from_digit;
#[allow(unused_imports)]
use std::cmp::{max, min};
#[allow(unused_imports)]
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
#[allow(unused_imports)]
use std::fs::File;
#[allow(unused_imports)]
use std::io::prelude::*;
#[allow(unused_imports)]
use std::io::{stdin, stdout, BufReader, BufWriter, Stdin, Stdout, Write};
#[allow(unused_imports)]
use std::mem::swap;
#[allow(unused_imports)]
use std::str::FromStr;
 
type BoxResult<T> = Result<T, Box<std::error::Error>>;
 
fn main() {
    let mut scanner = Scanner::new(stdin());
    let param = scanner.read_vector::<usize>().unwrap();
    let (h, _w) = (param[0], param[1]);
    let mut grid = vec![];
    let mut white = 0;
    for _ in 0..h {
        let s = scanner.read_chars().unwrap();
        for c in s.iter() {
            if *c == '.' {
                white += 1;
            }
        }
        grid.push(s);
    }
    if let Some(cost) = bfs(&grid) {
        println!("{}", white - 1 - cost);
    } else {
        println!("-1");
    }
}

fn bfs(grid: &[Vec<char>]) -> Option<usize> {
    let h = grid.len();
    let w = grid[0].len();
    let mut queue = VecDeque::new();
    let mut used = vec![vec![false; w]; h];
    queue.push_front((0, 0, 0));
    used[0][0] = true;
    let dir = [(-1, 0), (1, 0), (0, -1), (0, 1)];
    while queue.len() > 0 {
        let (x, y, c) = queue.pop_back().unwrap();
        if x == h - 1 && y == w - 1 {
            return Some(c);
        }
        for &(dx, dy) in dir.iter() {
            let new_x = x as i64 + dx;
            let new_y = y as i64 + dy;
            if new_x >= 0 && new_x < h as i64 && new_y >= 0 && new_y < w as i64 {
                let new_x = new_x as usize;
                let new_y = new_y as usize;
                if used[new_x][new_y] || grid[new_x][new_y] == '#' {
                    continue;
                }
                queue.push_front((new_x, new_y, c + 1));
                used[new_x][new_y] = true;
            }
        }
    }
    None
}


#[allow(dead_code)]
struct Scanner<R> {
    reader: BufReader<R>,
    buffer: String,
}
impl<R> Scanner<R>
where
    R: Read,
{
    #[allow(dead_code)]
    fn new(inner: R) -> Scanner<R> {
        let reader = BufReader::new(inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
    #[allow(dead_code)]
    fn with_capacity(capacity: usize, inner: R) -> Scanner<R> {
        let reader = BufReader::with_capacity(capacity, inner);
        let buffer = String::new();
        Scanner {
            reader: reader,
            buffer: buffer,
        }
    }
 
    #[allow(dead_code)]
    fn read_line(&mut self) -> BoxResult<String> {
        self.reader.read_line(&mut self.buffer)?;
        let cloned = self.buffer.trim().to_string();
        self.buffer.clear();
        Ok(cloned)
    }
 
    #[allow(dead_code)]
    fn read<T>(&mut self) -> BoxResult<T>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed = self.buffer.trim().parse()?;
        self.buffer.clear();
        Ok(parsed)
    }
    #[allow(dead_code)]
    fn read_vector<T>(&mut self) -> BoxResult<Vec<T>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        self.reader.read_line(&mut self.buffer)?;
        let parsed_vec = self
            .buffer
            .trim()
            .split_whitespace()
            .map(|s| s.parse())
            .collect::<Result<Vec<_>, _>>()?;
        self.buffer.clear();
        Ok(parsed_vec)
    }
    #[allow(dead_code)]
    fn read_matrix<T>(&mut self, lines: usize) -> BoxResult<Vec<Vec<T>>>
    where
        T: FromStr,
        T::Err: std::fmt::Debug,
        T::Err: std::error::Error,
        T::Err: 'static,
    {
        let mut parsed_matrix = vec![];
        for _ in 0..lines {
            self.reader.read_line(&mut self.buffer)?;
            parsed_matrix.push(
                self.buffer
                    .trim()
                    .split_whitespace()
                    .map(|s| s.parse())
                    .collect::<Result<Vec<_>, _>>()?,
            );
            self.buffer.clear();
        }
        Ok(parsed_matrix)
    }
    #[allow(dead_code)]
    fn read_chars(&mut self) -> BoxResult<Vec<char>> {
        self.reader.read_line(&mut self.buffer)?;
        let chars = self.buffer.trim().chars().collect::<Vec<_>>();
        self.buffer.clear();
        Ok(chars)
    }
}

Measured memory_bytes: 4352