#import pdb; pdb.set_trace()
import copy
import math

def main():
    (h, w) = map(int, input().split())
    
    s = []
    for i in range(h):
        s.append(list(map(int, list(input().replace("#", "1").replace(".", "0")))))
    
    depth = min(int(math.ceil(w / 2)), int(math.ceil(h / 2)))
    maxi = 1
    for k in range(1, depth):
        for j in range(k, depth):

            for i in range(1, w - j):
                a = j
                b = i
                if s[a][b] == k:
                    s[a][b] = min(s[a + 1][b + 1], s[a + 1][b], s[a + 1][b - 1], s[a][b - 1], s[a - 1][b - 1], s[a - 1][b], s[a - 1][b + 1], s[a][b + 1]) + 1
                    maxi = k 
            for i in range(1, h - j):
                a = i
                b = j
                if s[a][b] == k:
                    s[a][b] = min(s[a + 1][b + 1], s[a + 1][b], s[a + 1][b - 1], s[a][b - 1], s[a - 1][b - 1], s[a - 1][b], s[a - 1][b + 1], s[a][b + 1]) + 1
                    maxi = k 
            for i in range(1, w - j):
                a = h - 1 - j
                b = i
                if s[a][b] == k:
                    s[a][b] = min(s[a + 1][b + 1], s[a + 1][b], s[a + 1][b - 1], s[a][b - 1], s[a - 1][b - 1], s[a - 1][b], s[a - 1][b + 1], s[a][b + 1]) + 1
                    maxi = k 
            for i in range(1, h - j):
                a = i
                b = w - 1 - j
                if s[a][b] == k:
                    s[a][b] = min(s[a + 1][b + 1], s[a + 1][b], s[a + 1][b - 1], s[a][b - 1], s[a - 1][b - 1], s[a - 1][b], s[a - 1][b + 1], s[a][b + 1]) + 1
                    maxi = k 
    print(maxi)
    
if __name__ == '__main__':
    main()