#[allow(unused_macros)]
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)*}
    };
}

#[allow(unused_macros)]
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)*}
    };
}

#[allow(unused_macros)]
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<_>>()
    };

    ($next:expr, chars) => {
        read_value!($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 main() {
    input! {
        h: usize,
        w: usize,
        sij: [chars; h]
    }
    const MAX_COST: i64 = 99999;
    let mut costss = vec![vec![MAX_COST; w]; h];
    costss[0][0] = 0;
    loop {
        let mut update = false;
        for i in 0..h {
            for j in 0..w {
                if costss[i][j] != MAX_COST {
                    if i != 0 {
                        if sij[i - 1][j] == '.' {
                            if costss[i - 1][j] > costss[i][j] + 1 {
                                costss[i - 1][j] = costss[i][j] + 1;
                                update = true;
                            }
                        }
                    }
                    if j != 0 {
                        if sij[i][j - 1] == '.' {
                            if costss[i][j - 1] > costss[i][j] + 1 {
                                costss[i][j - 1] = costss[i][j] + 1;
                                update = true;
                            }
                        }
                    }
                    if i != h - 1 {
                        if sij[i + 1][j] == '.' {
                            if costss[i + 1][j] > costss[i][j] + 1 {
                                costss[i + 1][j] = costss[i][j] + 1;
                                update = true;
                            }
                        }
                    }
                    if j != w - 1 {
                        if sij[i][j + 1] == '.' {
                            if costss[i][j + 1] > costss[i][j] + 1 {
                                costss[i][j + 1] = costss[i][j] + 1;
                                update = true;
                            }
                        }
                    }
                }
            }
        }
        if !update {
            break;
        }
    }
    if costss[h - 1][w - 1] == MAX_COST {
        println!("-1");
    } else {
        let dot_count = {
            let mut count = 0;
            for items in sij {
                for item in items {
                    if item == '.' {
                        count += 1;
                    }
                }
            }
            count
        };
        let ans = dot_count - costss[h - 1][w - 1] - 1;
        println!("{}", ans);
    }
}


Measured memory_bytes: 4352