#![allow(non_snake_case)]
#![allow(dead_code)]
#![allow(unused_macros)]
#![allow(unused_imports)]

use std::str::FromStr;
use std::io::*;
use std::collections::*;
use std::cmp::*;

struct Scanner<I: Iterator<Item = char>> {
    iter: std::iter::Peekable<I>,
}

macro_rules! exit {
    () => {{
        exit!(0)
    }};
    ($code:expr) => {{
        if cfg!(local) {
            writeln!(std::io::stderr(), "===== Terminated =====")
                .expect("failed printing to stderr");
        }
        std::process::exit($code);
    }}
}

impl<I: Iterator<Item = char>> Scanner<I> {
    pub fn new(iter: I) -> Scanner<I> {
        Scanner {
            iter: iter.peekable(),
        }
    }

    pub fn safe_get_token(&mut self) -> Option<String> {
        let token = self.iter
            .by_ref()
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect::<String>();
        if token.is_empty() {
            None
        } else {
            Some(token)
        }
    }

    pub fn token(&mut self) -> String {
        self.safe_get_token().unwrap_or_else(|| exit!())
    }

    pub fn get<T: FromStr>(&mut self) -> T {
        self.token().parse::<T>().unwrap_or_else(|_| exit!())
    }

    pub fn vec<T: FromStr>(&mut self, len: usize) -> Vec<T> {
        (0..len).map(|_| self.get()).collect()
    }

    pub fn mat<T: FromStr>(&mut self, row: usize, col: usize) -> Vec<Vec<T>> {
        (0..row).map(|_| self.vec(col)).collect()
    }

    pub fn char(&mut self) -> char {
        self.iter.next().unwrap_or_else(|| exit!())
    }

    pub fn chars(&mut self) -> Vec<char> {
        self.get::<String>().chars().collect()
    }

    pub fn line(&mut self) -> String {
        if self.peek().is_some() {
            self.iter
                .by_ref()
                .take_while(|&c| !(c == '\n' || c == '\r'))
                .collect::<String>()
        } else {
            exit!();
        }
    }

    pub fn peek(&mut self) -> Option<&char> {
        self.iter.peek()
    }
}

trait Joinable {
    fn join(self, sep: &str) -> String;
}

impl<U: ToString, T: Iterator<Item = U>> Joinable for T {
    fn join(self, sep: &str) -> String {
        self.map(|x| x.to_string()).collect::<Vec<_>>().join(sep)
    }
}

fn main() {
    let cin = stdin();
    let cin = cin.lock();
    let mut sc = Scanner::new(cin.bytes().map(|c| c.unwrap() as char));
    let H: usize = sc.get();
    let W: usize = sc.get();
    let mut s: Vec<Vec<char>> = Vec::new();

    for _ in 0..H {
        let si = sc.chars();
        s.push(si);
    }
    let mut q = VecDeque::new();
    let mut v = vec![vec![-1; W]; H];

    let di = vec![0, -1, 0, 1];
    let dj = vec![1, 0, -1, 0];

    q.push_front((0, 0));
    v[0][0] = 0;
    while let Some((i, j)) = q.pop_back() {
        let cur = v[i][j];
        for d in 0..4 {
            let ni = i as i64 + di[d];
            let nj = j as i64 + dj[d];
            if ni < 0 || ni >= H as i64 || nj < 0 || nj >= W as i64 {
                continue;
            }
            let ni = ni as usize;
            let nj = nj as usize;
            if s[ni][nj] == '#' {
                continue;
            }
            if v[ni][nj] != -1 {
                continue;
            }
            v[ni][nj] = cur + 1;
            q.push_front((ni, nj));
        }
    }
    let (mut si, mut sj) = (H-1, W-1);
    if v[si][sj] == -1 {
        println!("-1");
        return;
    }
    let mut path = HashSet::new();
    while si != 0 || sj != 0 {
        let cur = v[si][sj];
        for d in 0..4 {
            let ni = si as i64 + di[d];
            let nj = sj as i64 + dj[d];
            if ni < 0 || ni >= H as i64 || nj < 0 || nj >= W as i64 {
                continue;
            }
            let ni = ni as usize;
            let nj = nj as usize;
            if v[ni][nj] == cur - 1 {
                path.insert((ni, nj));
                si = ni;
                sj = nj;
                break;
            }
        }
    }
    let mut ans = 0;
    for i in 0..H {
        for j in 0..W {
            if (i == 0 && j == 0) || (i == H-1 && j == W-1) {
                continue;
            }
            if !path.contains(&(i, j)) && s[i][j] == '.' {
                ans += 1;
            }
        }
    }
    println!("{}", ans);
}


Measured memory_bytes: 4352