#[allow(unused_imports)]
use std::collections::HashSet;

#[allow(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn main() {
    let hw = read_vec::<usize>();
    let h = hw[0];
    let w = hw[1];

    let mut shogai_yoko : Vec<Vec<(usize, usize)>> = Vec::with_capacity(h);
    let mut shogai_tate : Vec<Vec<(usize, usize)>> = Vec::with_capacity(w);
    for _i in 0..w {
        let u : Vec<(usize, usize)> = Vec::with_capacity(h);
        shogai_tate.push(u);
    }
    
    for i in 0..h {
        let mut v : Vec<(usize, usize)> = Vec::with_capacity(w);
        let s = read::<String>();
        let mut in_shogai_yoko = false;
        let mut in_shogai_tate = vec![false;w];
        for (j, c) in s.chars().enumerate() {
            if c == '#' {
                if in_shogai_yoko {
                    let last = v.last_mut().unwrap();
                    last.1 = last.1 + 1;
                } else {
                    v.push((j, j+1));
                    in_shogai_yoko = true;
                }

                let u = shogai_tate.get_mut(j).unwrap();
                if in_shogai_tate[j] {
                    let last = u.last_mut().unwrap();
                    last.1 = last.1 + 1;
                } else {
                    u.push((i, i+1));
                    in_shogai_tate[j] = true;
                }
            } else {
                if in_shogai_yoko {
                    in_shogai_yoko = false;
                } 
                if in_shogai_tate[j] {
                    in_shogai_tate[j] = false;
                }
            } 
        }
       
        if v.is_empty() || v[v.len()-1].1 < w {
            v.push((w, 0));
        }
        shogai_yoko.push(v);
    }
    for j in 0..w {
        let u = &mut shogai_tate[j];
        if u.is_empty() || u[u.len() - 1].1 < h {
            u.push((h, 0))
        }
    }


    let answer = solve(h, w, &shogai_yoko, &shogai_tate);
    println!("{}", answer);
}

fn solve(h: usize, w: usize, shogai_yoko: &[Vec<(usize, usize)>], shogai_tate: &[Vec<(usize, usize)>]) -> usize {
     // (yoko, tate)
     let mut dp : Vec<Vec<usize>> = vec![vec![0;w];h];

     // yoko
     for i in 0..h {
        let mut from = 0;
        for x in &shogai_yoko[i] {
            let d = x.0 - from;
            if d > 1 {
                for j in from..x.0 {
                    dp[i][j] = d - 1;
                }
            }
            from = x.1
        }
    }

    // tate (and total)
    let mut max = 0;
    let limit = (h-1) + (w-1);
    for j in 0..w {
        let mut from = 0;
        for x in &shogai_tate[j] {
            let d = x.0 - from;
            if d > 0 {
                let mut yoko_max = 0;
                for i in from..x.0 {
                    let yoko = dp[i][j];
                    if yoko > yoko_max {
                        yoko_max = yoko;
                    }
                }
                let val = yoko_max + (d - 1);
                if val > max {
                    max = val;
                    if max == limit {
                        return max + 1;
                    }
                }
            }
            from = x.1;
        }
    }
    return max + 1
}

Measured memory_bytes: 192764