#include <bits/stdc++.h>
using namespace std;

typedef long long   signed int LL;
typedef long long unsigned int LU;

#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); i++)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); i--)
#define  inc(i, n) incID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define  dec(i, n) decID(i, 0, n)
#define dec1(i, n) decII(i, 1, n)

#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))

#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define PQ priority_queue

#define  ALL(v)  v.begin(),  v.end()
#define RALL(v) v.rbegin(), v.rend()
#define  FOR(it, v) for(auto it =  v.begin(); it !=  v.end(); ++it)
#define RFOR(it, v) for(auto it = v.rbegin(); it != v.rend(); ++it)

template<typename T> bool   setmin(T & a, T b) { if(b <  a) { a = b; return true; } else { return false; } }
template<typename T> bool   setmax(T & a, T b) { if(b >  a) { a = b; return true; } else { return false; } }
template<typename T> bool setmineq(T & a, T b) { if(b <= a) { a = b; return true; } else { return false; } }
template<typename T> bool setmaxeq(T & a, T b) { if(b >= a) { a = b; return true; } else { return false; } }
template<typename T> T gcd(T a, T b) { return (b == 0 ? a : gcd(b, a % b)); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

// ---- ----

class UnionFind {
public:
	void init(int size);
	int unite(int v, int w);
	int find(int v);
	int get_size_eq(int v);
	int get_size_part();
	virtual ~UnionFind();

private:
	int *parent;
	int *size_eq;
	int size_part;
};

void UnionFind::init(int size) {
	parent = new int[size];
	size_eq = new int[size];
	for(int i = 0; i < size; i++) { parent[i] = -1; size_eq[i] = 1; }
	size_part = size;
}

int UnionFind::unite(int v, int w) {
	int fv = find(v);
	int fw = find(w);
	if(fv == fw) { return fv; }
	
	size_part--;
	int &sv = size_eq[fv];
	int &sw = size_eq[fw];
	
	if(sv < sw) {
		parent[fv] = fw;
		sw += sv;
		return fw;
	} else {
		parent[fw] = fv;
		sv += sw;
		return fv;
	}
}

int UnionFind::find(int v) {
	if(parent[v] == -1) { return v; }
	return parent[v] = find( parent[v] );
}

int UnionFind::get_size_eq(int v) {
	return size_eq[ find(v) ];
}

int UnionFind::get_size_part() {
	return size_part;
}

UnionFind::~UnionFind() {
	delete[] parent;
	delete[] size_eq;
}

// ----

#define UQ(v) v.erase(unique(ALL(v)), v.end())

int n, m;
string s[1003];
UnionFind uf;
vector<int> v[1003 * 1003];

pair<int, int> dfs(int pos, int par, int t) {
	auto p1 = MP(0, 0);
	inc(i, v[pos].size()) {
		if(v[pos][i] == par) { continue; }
		auto p2 = dfs(v[pos][i], pos, 1 - t);
		p1.FI += p2.FI;
		p1.SE += p2.SE;
	}
	if(t == 0) { return p1; }
	swap(p1.FI, p1.SE);
	p1.FI += uf.get_size_eq(pos);
	setmax(p1.FI, p1.SE);
	return p1;
}

int main() {
	cin >> n >> m;
	s[0] = s[1] = s[n + 2] = string(m + 3, '.');
	incID(i, 2, n + 2) { cin >> s[i]; s[i] = ".." + s[i] + "."; }
	s[0][0] = 'x';
	
	n += 3;
	m += 3;
	uf.init(n * m);
	vector<pair<int, int>> vp;
	int di[4] = { 0,  1, 1, 1 };
	int dj[4] = { 1, -1, 0, 1 };
	inc(q, 2) {
	inc(i, n) {
	inc(j, m) {
		inc(k, 4) {
			int ii = i + di[k]; if(! inID(ii, 0, n)) { continue; }
			int jj = j + dj[k]; if(! inID(jj, 0, m)) { continue; }
			if(q == 0) {
				if(
					(s[i][j] == 'x' && s[ii][jj] == 'x') ||
					(s[i][j] == '.' && s[ii][jj] == '.' && k % 2 == 0)
				) { uf.unite(m * i + j, m * ii + jj); }
			} else {
				if(s[i][j] != s[ii][jj]) {
					vp.EB(uf.find(m * i + j), uf.find(m * ii + jj));
					vp.EB(uf.find(m * ii + jj), uf.find(m * i + j));
				}
			}
		}
	}
	}
	}
	sort(ALL(vp));
	UQ(vp);
	inc(i, vp.size()) { v[vp[i].FI].PB(vp[i].SE); }
	
	cout << dfs(uf.find(m * 0 + 0), -1, 1).SE << endl;
	
	return 0;
}