use std::{collections::VecDeque, arch::x86_64::_MM_GET_ROUNDING_MODE};

const DX: [isize; 8] = [-1, -1, -1, 0, 0, 1, 1, 1];
const DY: [isize; 8] = [-1, 0, 1, -1, 1, -1, 0, 1];
const INF: u16 = 30000u16;

fn main() {
    let mut hw = String::new();
    std::io::stdin().read_line(&mut hw).ok();
    let hw: Vec<usize> = hw.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let h = hw[0];
    let w = hw[1];
    let mut grid = Vec::with_capacity(h+2);
    grid.push(vec![0u16; w+2]);
    for _ in 0..h {
        let mut line = vec![INF; w+2];
        line[0] = 0;
        line[w+1] = 0;
        let mut temp = String::new();
        std::io::stdin().read_line(&mut temp).ok();
        let temp = temp.trim().chars().collect::<Vec<_>>();
        for i in 0..w {
            if temp[i] == '.' {
                line[i+1] = 0;
            }
        }
        grid.push(line);
    }
    grid.push(vec![0u16; w+2]);

    let mut deque = VecDeque::new();
    for i in 1..=h {
        for j in 1..=w {
            if grid[i][j] == 0 { continue; }
            for dir in 0..8 {
                let nx = i as isize + DX[dir];
                let nx = nx as usize;
                let ny = j as isize + DY[dir];
                let ny = ny as usize;
                if grid[nx][ny] == 0 {
                    grid[i][j] = 1;
                    deque.push_back((i, j));
                    break;
                }
            }
        }
    }
    while let Some((i, j)) = deque.pop_front() {
        let nval = grid[i][j] + 1;
        for dir in 0..8 {
            let nx = i as isize + DX[dir];
            let nx = nx as usize;
            let ny = j as isize + DY[dir];
            let ny = ny as usize;
            if grid[nx][ny] > nval {
                grid[nx][ny] = nval;
                deque.push_back((nx, ny));
            }
        }
    }
// for v in grid.iter() { eprintln!("{:?}", v.iter().map(|j| j.to_string()).collect::<Vec<_>>().join("")); }
    println!("{}", grid.iter().map(|v| v.iter().max().unwrap()).max().unwrap());
}