#![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 main() {
    input! {
        h: usize, w: usize,
        s: [chars; h],
    }
    let mut L = vec![vec![0; w]; h];
    let mut R = vec![vec![0; w]; h];
    let mut U = vec![vec![0; w]; h];
    let mut D = vec![vec![0; w]; h];

    // L
    for h_ in 0..h {
        for w_ in 0..w {
            if s[h_][w_] == '#' {
                L[h_][w_] = 0
            } else if w_ == 0 {
                L[h_][w_] = 1;
            } else {
                L[h_][w_] = L[h_][w_ - 1] + 1;
            }
        }
    }

    // R
    for h_ in 0..h {
        for w_ in (0..w).rev() {
            if s[h_][w_] == '#' {
                R[h_][w_] = 0
            } else if w_ == w - 1 {
                R[h_][w_] = 1;
            } else {
                R[h_][w_] = R[h_][w_ + 1] + 1;
            }
        }
    }

    // D
    for h_ in 0..h {
        for w_ in 0..w {
            if s[h_][w_] == '#' {
                D[h_][w_] = 0
            } else if h_ == 0 {
                D[h_][w_] = 1;
            } else {
                D[h_][w_] = D[h_ - 1][w_] + 1;
            }
        }
    }
    // U
    for h_ in (0..h).rev() {
        for w_ in 0..w {
            if s[h_][w_] == '#' {
                U[h_][w_] = 0
            } else if h_ == h - 1 {
                U[h_][w_] = 1;
            } else {
                U[h_][w_] = U[h_ + 1][w_] + 1;
            }
        }
    }

    let mut ans = 0;
    for h_ in 0..h {
        for w_ in 0..w {
            ans = max(ans, U[h_][w_] + D[h_][w_] + L[h_][w_] + R[h_][w_] - 3)
        }
    }
    println!("{}", ans);
}


Measured memory_bytes: 86268