#include <bits/stdc++.h>
using namespace std;
int main(int, char const *[])
{
  int n, m;
  cin >> n >> m;
  vector<string> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];
  vector<vector<int>> G(n * m + 1);
  vector<int> color(n * m + 1, -1);
  vector<int> match(n * m + 1);
  vector<int> vis(n * m + 1);
  function<int(int, int)> index = [&](int x, int y)
  {
    return x * m + y + 1;
  };
  function<void(int, int)> addEdge = [&](int u, int v)
  {
    G[u].push_back(v);
    G[v].push_back(u);
    return;
  };
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++)
    {
      if (a[i][j] == 'x')
        continue;
      int x = index(i, j);
      if (i != 0 && a[i - 1][j] != 'x')
        addEdge(x, index(i - 1, j));
      if (j != 0 && a[i][j - 1] != 'x')
        addEdge(x, index(i, j - 1));
    }
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++)
    {
      int u = index(i, j);
      sort(G[u].begin(), G[u].end());
    }
  function<bool(int, int)> dfs = [&](int u, int tag)
  {
    if (vis[u] == tag)
      return false;
    vis[u] = tag;
    for (auto v : G[u])
    {
      if (!match[v] || dfs(match[v], tag))
      {
        match[v] = u;
        return true;
      }
    }
    return false;
  };
  int ans = 0;
  for (int i = 1; i <= n * m; i++)
    if (dfs(i, i))
      ans++;
  cout << (ans >> 1);
  return 0;
}