#[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],
    }

    let mut start;
    let mut end;
    // make horizontal table
    let mut hori_table = vec![vec![0; w]; h];
    for i in 0..h {
        start = 0;
        for j in 0..w {
           if board[i][j] == '#' {
                end = j;
                for k in start..end {
                    hori_table[i][k] = end - start;
                }
                start = end + 1;
           }
           if j == w-1 {
               end = j+1;
               for k in start..end {
                   hori_table[i][k] = end - start;
               }
           }
        }
    }

    let mut ver_table = vec![vec![0; h]; w];
    for i in 0..w {
        start = 0;
        for j in 0..h {
           if board[j][i] == '#' {
                end = j;
                for k in start..end {
                    ver_table[i][k] = end - start;
                }
                start = end + 1;
           }
           if j == h-1 {
               end = j+1;
               for k in start..end {
                    ver_table[i][k] = end - start;
               }
           }
        }
    }

    /*
    for i in 0..h {
        println!("{:?}", hori_table[i]);
    }
    for i in 0..w {
        println!("{:?}", ver_table[i]);
    }
    */
    let mut max = 0;

    for i in 0..h {
        for j in 0..w {
            let t = hori_table[i][j] + ver_table[j][i];
            if max < t {
                max = t;
            }
        }
    }

    println!("{}", max-1);
}


Measured memory_bytes: 102652