#![allow(non_snake_case, unused)]
use std::cmp::*;
use std::collections::*;
use std::f64::consts::*;

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };

    ($next:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, [ $t:tt ]) => {
        {
            let len = read_value!($next, usize);
            (0..len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
        }
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}

fn adjacent_4(x: usize, y: usize, h: usize, w: usize) -> Vec<(usize, usize)> {
    [(0, 1), (1, 0), (0, -1), (-1, 0)]
        .into_iter()
        .filter_map(|&(dy, dx)| {
            let x_ = x as isize + dx;
            let y_ = y as isize + dy;
            if 0 <= x_ && x_ < w as isize && 0 <= y_ && y_ < h as isize {
                Some((x_ as usize, y_ as usize))
            } else {
                None
            }
        })
        .collect()
}

fn main() {
    input! {
        h: usize, w: usize,
        s: [chars; h],
    }
    let mut w_cnt = 0;
    for h_ in 0..h {
        for w_ in 0..w {
            if s[h_][w_] == '.' {
                w_cnt += 1;
            }
        }
    }

    let mut dist = vec![vec![-1; w]; h];
    dist[0][0] = 1;
    let mut que = VecDeque::new();
    que.push_back((0, 0));

    while !que.is_empty() {
        let (w_, h_) = que.pop_front().unwrap();
        for (w__, h__) in adjacent_4(w_, h_, h, w) {
            if dist[h__][w__] == -1 && s[h__][w__] == '.' {
                dist[h__][w__] = dist[h_][w_] + 1;
                que.push_back((w__, h__));
            }
        }
    }
    if dist[h - 1][w - 1] == -1 {
        println!("-1");
    } else {
        println!("{}", w_cnt - dist[h - 1][w - 1]);
    }
}


Measured memory_bytes: 4352