from itertools import *
from bisect import *
from collections import *
from heapq import *
import sys

sys.setrecursionlimit(10 ** 6)

def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def SI(): return sys.stdin.readline()[:-1]
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
int1 = lambda x: int(x) - 1
def MI1(): return map(int1, sys.stdin.readline().split())
def LI1(): return list(map(int1, sys.stdin.readline().split()))
p2D = lambda x: print(*x, sep="\n")
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

class Dinic():
    def __init__(self, n, s, t):
        self.n, self.s, self.t = n, s, t
        self.to = defaultdict(list)
        self.level = [-1]
        self.max_flow = -1

    def add_edge(self, u, v, cap):
        u_index_in_to_v = len(self.to[v])
        v_index_in_to_u = len(self.to[u])
        self.to[u].append([v, cap, u_index_in_to_v])
        self.to[v].append([u, 0, v_index_in_to_u])

    # 無向辺の追加
    def add_undir_edge(self, u, v, cap):
        u_index_in_to_v = len(self.to[v])
        v_index_in_to_u = len(self.to[u])
        self.to[u].append([v, cap, u_index_in_to_v])
        self.to[v].append([u, cap, v_index_in_to_u])

    def set_level(self):
        s = self.s
        level = [-1] * self.n
        level[s] = 0
        q = deque()
        q.append([s, 0])
        while q:
            u, u_level = q.popleft()
            for v, cap, _ in self.to[u]:
                if cap == 0: continue
                if level[v] != -1: continue
                level[v] = u_level + 1
                if v == self.t:
                    self.level = level
                    return True
                q.append([v, u_level + 1])
        return False

    def dfs(self, u=-1, flow_to_me=10 ** 16):
        if u == -1: u = self.s
        if u == self.t: return flow_to_me
        flow_from_me = 0
        u_level = self.level[u]
        for utov_i, (v, cap, vtou_i) in enumerate(self.to[u]):
            if self.level[v] != u_level + 1: continue
            if cap == 0: continue
            flow_to_v = self.dfs(v, min(cap, flow_to_me - flow_from_me))
            if not flow_to_v: continue
            flow_from_me += flow_to_v
            self.to[u][utov_i][1] -= flow_to_v
            self.to[v][vtou_i][1] += flow_to_v
        return flow_from_me

    def calculation(self):
        res = 0
        while self.set_level():
            res += self.dfs()
        return res

    # これが出力用
    def get_max_flow(self):
        if self.max_flow == -1:
            self.max_flow = self.calculation()
        return self.max_flow

def main():
    h,w=MI()
    ss=[SI() for _ in range(h)]
    aa=[[0]*w for _ in range(h)]
    # 始点を頂点0、終点を頂点1とするので、W,Bに2から頂点番号を振っていく
    cnt=2
    for i,j in product(range(h),range(w)):
        if ss[i][j]==".":continue
        aa[i][j]=cnt
        cnt+=1
    # 最大流のライブラリ
    mf=Dinic(cnt,0,1)
    # それぞれのマスから右と下に辺を張るとともにw,bの数を数える
    wc=bc=0
    for i,j in product(range(h),range(w)):
        a=aa[i][j]
        if a==0:continue
        # 黒のとき（2部グラフの右側）
        if (i+j)%2:
            bc+=1
            mf.add_edge(a,1,1)
            if j+1<w and aa[i][j+1]:mf.add_edge(aa[i][j+1],a,1)
            if i+1<h and aa[i+1][j]:mf.add_edge(aa[i+1][j],a,1)
        # 白のとき（2部グラフの左側）
        else:
            wc+=1
            mf.add_edge(0,a,1)
            if j+1<w and aa[i][j+1]:mf.add_edge(a,aa[i][j+1],1)
            if i+1<h and aa[i+1][j]:mf.add_edge(a,aa[i+1][j],1)
    # ペアの組数がp
    p=mf.get_max_flow()
    wc,bc=wc-p,bc-p
    mn=min(wc,bc)
    ans=p*100+mn*10+wc+bc-2*mn
    print(ans)

main()