W,H=map(int,input().split())
pa=[[[0,-1][x=='#'] for x in input()] for y in range(H)]

def fx(y,x,na,nb):
    if not 0<=y<H:      return 0
    if not 0<=x<W:      return 0
    n=pa[y][x]
    if n>=nb:           return 0
    if n> na:           return 1
    pa[y][x]=nb
    if n<0:             return 0
    if fx(y-1,x,na,nb): return 1
    if fx(y+1,x,na,nb): return 1
    if fx(y,x-1,na,nb): return 1
    if fx(y,x+1,na,nb): return 1
    return 0

def fy():
    nb=0
    for na in range(20):
        for y in range(H):
            for x in range(W):
                n=pa[y][x]
                if n==na:
                    if fx(y,x,na,nb):   return nb-1
                    nb+=1
        if nb-na<=2:     return nb-na-1
    return 1

print(fy())