import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv, std.math,
    std.functional, std.numeric, std.range, std.stdio, std.string, std.random,
    std.typecons, std.container;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
// dfmt on

void main()
{
    long H, W;
    scan(H, W);
    long[2][] black;
    long[2][] white;
    foreach (i; 0 .. H)
    {
        auto A = sread();
        foreach (j, c; A)
            if (c == '#')
            {
                black ~= [i, j];
            }
            else
            {
                white ~= [i, j];
            }
    }

    long ans = long.min;
    foreach (w; white)
    {
        long tmp = long.max;
        foreach (b; black)
        {
            tmp = tmp.min(abs(w[0] - b[0]) + abs(w[1] - b[1]));
        }
        ans = ans.max(tmp);
    }
    writeln(ans);
}
