#Dinic法で最大流を求める
#deque のimport が必要
#逆辺追加しなきゃいけないから、
#グラフの構成はadd_edgeで行う
#最大流は　flow    メソッドで

from collections import deque
class Dinic:
    def __init__(self,N):
        self.N = N
        self.G = [[] for _ in range(N)]
        self.edge = []
    def add_edge(self,fr,to,cap):
        forward = [to,cap,None]
        forward[2] = backward = [fr,0,forward]
        self.G[fr].append(forward)
        self.G[to].append(backward)
        self.edge.append(forward)
    def add_multi_edge(self,v1,v2,cap1,cap2):
        edge1 = [v2,cap1,None]
        edge1[2] = edge2 = [v1,cap2,edge1]
        self.G[v1].append(edge1)
        self.G[v2].append(edge2)
        self.edge.append(edge1)
    def get_edge(self,i):
        return self.edge[i]
        # i 回目に追加した辺のポインタを返す
        # 0-index, 順辺のみ

    def bfs(self,s,t):
        self.level = level = [None] * self.N
        q = deque([s])
        level[s] = 0
        G = self.G
        while q:
            v = q.popleft()
            lv = level[v] + 1
            for w,cap,_ in G[v]:
                if cap and level[w] is None:
                    level[w] = lv
                    q.append(w)
        return level[t] is not None
    def dfs(self, v, t, f):
        if v == t:
            return f
        level = self.level
        for e in self.it[v]:
            w, cap, rev = e
            if cap and level[v] < level[w]:
                d = self.dfs(w, t, min(f, cap))
                if d:
                    e[1] -= d
                    rev[1] += d
                    return d
                else:
                    pass
            else:
                pass
        return 0

    def flow(self, s, t):
        flow = 0
        INF = 10**9 + 7
        G = self.G
        while self.bfs(s, t):
            *self.it, = map(iter, self.G)
            f = INF
            while f:
                f = self.dfs(s, t, INF)
                flow += f
        return flow
    def min_cut(self,s):
        #最小カットを実現する頂点の分割を与える
        #True  なら　source側
        #False なら　sink側
        visited = [False for i in range(self.N)]
        q = deque([s])
        while q:
            now = q.popleft()
            visited[now] = True
            for to,cap,_ in self.G[now]:
                if cap and not visited[to]:
                    visited[to] = True
                    q.append(to)
        return visited
    


    
import sys
rr = sys.stdin
H,W = map(int,rr.readline().split())
A = [list(map(int,rr.readline().split())) for _ in range(H)]


d = [[] for _ in range(5 * 10 ** 5 + 1)]
s = set()
for h in range(H):
    for w in range(W):
        d[A[h][w]].append((h,w))
        s.add(A[h][w])
        
inf = 1 << 30
ans = 0
for k in s:
    if k == 0:continue
    
    l = d[k]
    if len(l) == 1:
        ans += 1
        continue
    elif len(l) == 2:
        if l[0][0] == l[1][0] or l[0][1] == l[1][1]:
            ans += 1
        else:
            ans += 2
        continue
    ch = set()
    cw = set()
    for h,w in l:
        ch.add(h)
        cw.add(w)
    rDh = sorted(ch)
    rDw = sorted(cw)
    Dh = {v:i for i,v in enumerate(rDh)}
    Dw = {v:i for i,v in enumerate(rDw)}
    n = len(Dh) + len(Dw)
    dinic = Dinic(n + 2)
    T = n + 1
    base = len(Dh)
    for h,w in l:
        dinic.add_edge(Dh[h]+1,base + Dw[w] + 1,inf)
    for i in range(base):
        dinic.add_edge(0,i+1,1)
    for i in range(len(Dw)):
        dinic.add_edge(base + i + 1,T,1)
    ans += dinic.flow(0,T)
print(ans)