import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(1000005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = -1-(-1 << 63)
# md = 10**9+7
md = 998244353

def RLE(s):
    kk=[]
    vv=[]
    for c in s:
        if kk and kk[-1]==c:
            vv[-1]+=1
        else:
            kk.append(c)
            vv.append(1)
    return kk,vv

h,w=LI()
ss=[[c=="#" for c in SI()] for _ in range(h)]

ans=inf
for _ in range(2):
    for i in range(h):
        kk,vv=RLE(ss[i])
        for k,v in zip(kk,vv):
            if k:ans=min(ans,v)
    ss=[col for col in zip(*ss)]

print(ans)