#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef pair<ll, int> pli;
typedef array<int, 3> ai3;
const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3fll;
const int Mod = 1e9 + 7;
inline int sign(int a){ return (a&1) ? (Mod-1) : 1; }
inline void uadd(int &a, int b){ a += b-Mod; a += (a>>31) & Mod; }
inline void usub(int &a, int b){ a -= b, a += (a>>31) & Mod; }
inline void umul(int &a, int b){ a = (int)(1ll * a * b % Mod); }
inline int add(int a, int b){ a += b-Mod; a += (a>>31) & Mod; return a; }
inline int sub(int a, int b){ a -= b, a += (a>>31) & Mod; return a; }
inline int mul(int a, int b){ a = (int)(1ll * a * b % Mod); return a; }
int qpow(int b, ll p){ int ret = 1; while(p){ if(p&1) umul(ret, b); umul(b, b), p >>= 1; } return ret; }
const int fN = 100;
int fact[fN], invfact[fN], pw2[fN], invpw2[fN], inv[fN];
void initfact(int n){
	pw2[0] = 1; for(int i = 1; i <= n; ++i) pw2[i] = mul(pw2[i-1], 2);
	invpw2[0] = 1; for(int i = 1; i <= n; ++i) invpw2[i] = mul(invpw2[i-1], (Mod+1) / 2);
	fact[0] = 1; for(int i = 1; i <= n; ++i) fact[i] = mul(fact[i-1], i);
	invfact[n] = qpow(fact[n], Mod-2); for(int i = n; i > 0; --i) invfact[i-1] = mul(invfact[i], i);
	for(int i = 1; i <= n; ++i) inv[i] = mul(invfact[i], fact[i-1]);
}
int binom(int n, int m){ return (m < 0 || m > n) ? 0 : mul(fact[n], mul(invfact[m], invfact[n-m])); }
const ld pi = acos(-1);
inline void chmax(int &a, int b){ (b>a) ? (a=b) : 0; }
inline void chmin(int &a, int b){ (b<a) ? (a=b) : 0; }

namespace mf{
	int cn, cur[1000100], hd[1000100]; int dis[1000100];
	int ce, to[1000100], nxt[1000100]; int cap[1000100];
	void clr(int n){
		//cout << "------clr-------" << endl;
		cn = n, ce = 0;
		fill(hd, hd+cn, -1);
	}
	void ae(int f, int t, int c){
		//cout << "ae " << f << " " << t << " " << c << " " << inf-c << endl;
		nxt[ce] = hd[f], cap[ce] = c, to[ce] = t, hd[f] = ce++;
		nxt[ce] = hd[t], cap[ce] = 0, to[ce] = f, hd[t] = ce++;
	}
	bool bfs(int S, int T, int tp = 0){
		fill(dis, dis+cn, inf);
		dis[S] = 0;
		queue<int> q;
		q.emplace(S);
		while(!q.empty()){
			int u = q.front(); q.pop();
			//cout << "bfs " << u << endl;
			for(int eid = hd[u]; eid >= 0; eid = nxt[eid]){
				int t = to[eid];
				if(((tp == 0 && cap[eid]) || (tp == 1 && cap[eid^1])) && dis[t] > dis[u] + 1){
					dis[t] = dis[u] + 1;
					q.emplace(t);
				}
			}
		}
		//cout << cn << " " << S << " " << T << ": " << dis[T] << endl;
		return dis[T] < inf;
	}
	int dfs(int u, int dest, int flow){
		//cout << "dfs " << u << endl;
		if(u == dest) return flow;
		int nf = flow;
		for(int &eid = cur[u]; eid >= 0; eid = nxt[eid]){
			int t = to[eid];
			if(cap[eid] && dis[t] == dis[u] + 1){
				int ret = dfs(t, dest, min(nf, cap[eid]));
				nf -= ret, cap[eid] -= ret, cap[eid^1] += ret;
				if(!nf) break;
			}
		}
		return flow - nf;
	}
	int mf(int S, int T){
		int ans = 0;
		while(bfs(S, T)){
			rep(i, cn) cur[i] = hd[i];
			ans += dfs(S, T, inf);
			//cout << ans << endl;
		}
		return ans;
	}
}

int n, m;
string s[55];
int cc = 0, id[55][55];
const int dx[] = {-1, 0, 1, 0}, dy[] = {0, -1, 0, 1};

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> n >> m;
	rep(i, n) cin >> s[i];
	rep(i, n) rep(j, m) if(s[i][j] == '.') id[i][j] = cc++;

	mf::clr(2 + cc);
	
	rep(i, n) rep(j, m) if(s[i][j] == '.'){
		if((i+j) % 2 == 0) mf::ae(0, 2 + id[i][j], 1);
		else mf::ae(2 + id[i][j], 1, 1);
	}

	rep(i, n) rep(j, m) if(s[i][j] == '.' && (i+j) % 2 == 0) rep(dir, 4){
		int nx = i + dx[dir], ny = j + dy[dir];
		if(nx >= 0 && ny >= 0 && nx < n && ny < m && s[nx][ny] == '.'){
			mf::ae(2 + id[i][j], 2 + id[nx][ny], 1);
		}
	}

	mf::mf(0, 1);

	int ans = 0;
	rep(i, n) rep(j, m) if(s[i][j] == '.' && (i+j) % 2 == 0) ans += (mf::dis[2 + id[i][j]] < inf);
	mf::bfs(1, 0, 1);
	rep(i, n) rep(j, m) if(s[i][j] == '.' && (i+j) % 2 == 1) ans += (mf::dis[2 + id[i][j]] < inf);
	cout << ans << "\n";

	return 0;
}