/* imports all std modules {{{*/
import
  std.algorithm,
  std.array,
  std.ascii,
  std.base64,
  std.bigint,
  std.bitmanip,
  std.compiler,
  std.complex,
  std.concurrency,
  std.container,
  std.conv,
  std.csv,
  std.datetime,
  std.demangle,
  std.encoding,
  std.exception,
  std.file,
  std.format,
  std.functional,
  std.getopt,
  std.json,
  std.math,
  std.mathspecial,
  std.meta,
  std.mmfile,
  std.net.curl,
  std.net.isemail,
  std.numeric,
  std.parallelism,
  std.path,
  std.process,
  std.random,
  std.range,
  std.regex,
  std.signals,
  std.socket,
  std.stdint,
  std.stdio,
  std.string,
  std.system,
  std.traits,
  std.typecons,
  std.uni,
  std.uri,
  std.utf,
  std.uuid,
  std.variant,
  std.zip,
  std.zlib;
/*}}}*/

/* libnum {{{*/
void amax(N, Args...)(ref N x, Args y) {
  x = x.max(y);
}
void amin(N, Args...)(ref N x, Args y) {
  x = x.min(y);
}
auto maxE(R)(R r) if (isInputRange!R) {
  ElementType!R x = r.front;
  r.popFront();
  foreach (y; r) x.amax(y);
  return x;
}
auto minE(R)(R r) if (isInputRange!R) {
  ElementType!R x = r.front;
  r.popFront();
  foreach (y; r) x.amin(y);
  return x;
}
/*}}}*/

/+---test
3 3
...
.#.
...
---+/
/+---test
6 6
..#..#
......
#..#..
......
.#....
....#.
---+/

void main(string[] args) {
  long H, W;
  readf(" %d %d ", &H, &W);

  auto M = new ubyte[][](H);
  foreach (ref m; M) {
    m = readln.chomp.map!(to!ubyte).array;
  }

  struct Point { long x, y, cnt; }

  DList!Point q;

  foreach (y; 0..H) foreach (x; 0..W) {
    if (M[y][x] == '#') q.insertBack(Point(x, y));
  }

  long ans;
  while (!q.empty) {
    const p = q.front;
    q.removeFront;

    if (p.y < 0 || p.y >= H || p.x < 0 || p.x >= W) continue;
    if (M[p.y][p.x] == '#' && p.cnt > 0) continue;

    M[p.y][p.x] = '#';
    ans.amax(p.cnt);

    q.insertBack(Point(p.x, p.y-1, p.cnt+1));
    q.insertBack(Point(p.x, p.y+1, p.cnt+1));
    q.insertBack(Point(p.x-1, p.y, p.cnt+1));
    q.insertBack(Point(p.x+1, p.y, p.cnt+1));
  }
  ans.writeln;
}
