#[allow(unused_imports)]
use std::char::*;
#[allow(unused_imports)]
use std::cmp::*;
#[allow(unused_imports)]
use std::collections::*;
use std::io::*;
use std::str::FromStr;

#[allow(unused_macros)]
macro_rules! debug {($($a:expr),*) => {println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);}}
#[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 ) * } } ; }
#[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 , usize1 ) => { read_value ! ( $ next , usize ) - 1 } ; ( $ next : expr , $ t : ty ) => { $ next ( ) . parse ::<$ t > ( ) . expect ( "Parse error" ) } ; }

#[derive(PartialEq, PartialOrd)]
pub struct Total<T>(pub T);
impl<T: PartialEq> Eq for Total<T> {}
impl<T: PartialOrd> Ord for Total<T> { fn cmp(&self, other: &Total<T>) -> std::cmp::Ordering { self.0.partial_cmp(&other.0).unwrap() }}

#[allow(dead_code)]
const MAX:usize = 100006;
#[allow(dead_code)]
const INF:i64 = std::i64::MAX;
#[allow(dead_code)]
const MOD:i64 = 1e9 as i64 + 7;


#[allow(dead_code)]
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

#[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()
}


#[allow(unused_imports)]
use std::f64;

#[allow(dead_code)]
fn min<T: PartialOrd>(a:T, b:T) -> T {
    if a < b { a }
    else { b }
}
#[allow(dead_code)]
fn max<T: PartialOrd>(a:T, b:T) -> T {
    if a < b { b }
    else { a }
}

use std::hash::Hash;
#[allow(dead_code)]
fn inc<T: Hash+Ord>(map:&mut BTreeMap<T,i64>, key:T) {
    let count = map.entry(key).or_insert(0);
    *count += 1;
}

pub trait BinarySearch<T> {
    fn lower_bound(&self, x: &T) -> usize;
    fn upper_bound(&self, x: &T) -> usize;
}

impl<T: Ord> BinarySearch<T> for [T] {
    fn lower_bound(&self, x: &T) -> usize {
        let mut low = 0;
        let mut high = self.len();

        while low != high {
            let mid = (low + high) / 2;
            match self[mid].cmp(x) {
                Ordering::Less => {
                    low = mid + 1;
                }
                Ordering::Equal | Ordering::Greater => {
                    high = mid;
                }
            }
        }
        low
    }

    fn upper_bound(&self, x: &T) -> usize {
        let mut low = 0;
        let mut high = self.len();

        while low != high {
            let mid = (low + high) / 2;
            match self[mid].cmp(x) {
                Ordering::Less | Ordering::Equal => {
                    low = mid + 1;
                }
                Ordering::Greater => {
                    high = mid;
                }
            }
        }
        low
    }
}

fn main() {
    input!{h:usize, w:usize, s:[chars;h]};
    let mut v = vec![vec![];h];
    let mut u = vec![vec![];w];

    for i in 0..h {
        for j in 0..w {
            if s[i][j] == '#' {
                v[i].push(j+1);
                u[j].push(i+1);
            }
        }
    }
    for i in 0..h {
        v[i].push(0);
        v[i].push(w+1);
        v[i].sort();
    }
    for i in 0..w {
        u[i].push(0);
        u[i].push(h+1);
        u[i].sort();
    }
    //debug!(v);
    //debug!(u);

    let mut ans = 0;
    for i in 0..h {
        for j in 0..w {
            if s[i][j] == '.' {
                //debug!(i,j);
                let wl;
                if v[i].is_empty() {
                    wl = w;
                }
                else {
                    let idx1 = v[i].lower_bound(&(j+1));
                    let idx2 = v[i].upper_bound(&(j+1)) - 1;
                    wl = v[i][idx1] - v[i][idx2] + 1;
                }
                let hl;
                if u[j].is_empty() {
                    hl = h;
                }
                else {
                    let idx1 = u[j].lower_bound(&(i+1));
                    let idx2 = u[j].upper_bound(&(i+1)) - 1;
                    hl = u[j][idx1] - u[j][idx2] + 1;
                }
                let count = (wl+hl-5) as i64;
                //debug!(wl,hl,count);
                ans = max(ans, count);
            }
        }
    }

    println!("{}", ans);
}


Measured memory_bytes: 106748