#[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,
        board: [chars;h],
    }
    // println!("{:?}", board);
    let mut U = vec![vec![0;w];h];
    let mut D = vec![vec![0;w];h];
    let mut L = vec![vec![0;w];h];
    let mut R = vec![vec![0;w];h];
    
    for wi in 0..w {
        for hi in 0..h {
            if board[hi][wi]=='.' {
                if hi == 0 {
                    U[hi][wi] = 1;
                    continue;
                }
                U[hi][wi] =U[hi-1][wi]+1;
            }else{
                U[hi][wi] = 0;
            }
        }
    }
    for wi in 0..w {
        for hi in (0..h).rev() {
            if board[hi][wi]=='.' {
                if hi == h-1 {
                    D[hi][wi] = 1;
                    continue;
                }
                D[hi][wi] =D[hi+1][wi]+1;
            }else{
                D[hi][wi] = 0;
            }
        }
    }
    for hi in 0..h {
        for wi in 0..w {
            if board[hi][wi]=='.' {
                if wi == 0 {
                    L[hi][wi] = 1;
                    continue;
                }
                L[hi][wi] =L[hi][wi-1]+1;
            }else{
                L[hi][wi] = 0;
            }
        }
    }
    for hi in 0..h {
        for wi in (0..w).rev() {
            if board[hi][wi]=='.' {
                if wi == w-1 {
                    R[hi][wi] = 1;
                    continue;
                }
                R[hi][wi] =R[hi][wi+1]+1;
            }else{
                R[hi][wi] = 0;
            }
        }
    }
    let mut ans = 0;
    for hi in 0..h {
        for wi in 0..w {
            if board[hi][wi] == '.' {
                let sum = L[hi][wi] + U[hi][wi] + R[hi][wi] + D[hi][wi] - 3;
                ans = std::cmp::max(ans, sum);
            }
        }
    }
    println!("{}", ans);
}

Measured memory_bytes: 86268