import std.algorithm, std.conv, std.range, std.stdio, std.string;

alias point = Point!int;
alias grid = Grid!(bool, int);
alias graph = Graph!(int, int);
alias edge = graph.Edge;

void main()
{
  auto rd = readln.split.to!(int[]), r = rd[0], c = rd[1], n = r*c;
  auto g = grid(r, c);

  foreach (i; 0..r) {
    auto s = readln.chomp;
    foreach (j; 0..c)
      g[i][j] = s[j] != '.';
  }

  auto idx(point p) { return p.y*c+p.x; }
  auto h = new edge[][](n+2), nw = 0, nb = 0;

  foreach (i; 0..r)
    foreach (j; 0..c) {
      auto p = point(j, i);
      if ((i+j) % 2 == 0 && g[i][j]) {
        ++nw;
        h[n] ~= edge(n, idx(p), 1);
        foreach (np; g.sibPoints4(p).filter!(np => g[np]))
          h[idx(p)] ~= edge(idx(p), idx(np), 1);
      } else if ((i+j) % 2 == 1 && g[i][j]) {
        ++nb;
        h[idx(p)] ~= edge(idx(p), n+1, 1);
      }
    }

  auto w1 = graph.fordFulkerson(h, n, n+1);
  nw -= w1;
  nb -= w1;

  auto w2 = min(nw, nb);
  nw -= w2;
  nb -= w2;

  writeln(w1 * 100 + w2 * 10 + nw + nb);
}

struct Point(T)
{
  T x, y;
  pure auto opBinary(string op: "+")(Point!T rhs) const { return Point!T(x + rhs.x, y + rhs.y); }
  pure auto opBinary(string op: "-")(Point!T rhs) const { return Point!T(x - rhs.x, y - rhs.y); }
  pure auto opBinary(string op: "*")(Point!T rhs) const { return x * rhs.x + y * rhs.y; }
  pure auto opBinary(string op: "*")(T a) const { return Point!T(x * a, y * a); }
  pure auto opBinary(string op: "/")(T a) const { return Point!T(x / a, y / a); }
  pure auto hypot2() const { return x ^^ 2 + y ^^ 2; }
}

struct Grid(T, U)
{
  import std.algorithm, std.conv, std.range, std.traits, std.typecons;

  const sibs4 = [Point!U(-1, 0), Point!U(0, -1), Point!U(1, 0), Point!U(0, 1)];
  const sibs8 = [Point!U(-1, 0), Point!U(-1, -1), Point!U(0, -1), Point!U(1, -1),
                 Point!U(1, 0), Point!U(1, 1), Point!U(0, 1), Point!U(-1, 1)];

  T[][] m;
  const size_t rows, cols;

  mixin Proxy!m;

  this(size_t r, size_t c) { rows = r; cols = c; m = new T[][](rows, cols); }
  this(T[][] s) { rows = s.length; cols = s[0].length; m = s; }

  pure auto dup() const { return Grid(m.map!(r => r.dup).array); }
  ref pure auto opIndex(Point!U p) { return m[p.y][p.x]; }
  ref pure auto opIndex(size_t y) { return m[y]; }
  ref pure auto opIndex(size_t y, size_t x) const { return m[y][x]; }
  static if (isAssignable!T) {
    auto opIndexAssign(T v, Point!U p) { return m[p.y][p.x] = v; }
    auto opIndexAssign(T v, size_t y, size_t x) { return m[y][x] = v; }
    auto opIndexOpAssign(string op, V)(V v, Point!U p) { return mixin("m[p.y][p.x] " ~ op ~ "= v"); }
    auto opIndexOpAssign(string op, V)(V v, size_t y, size_t x) { return mixin("m[y][x] " ~ op ~ "= v"); }
  }
  pure auto validPoint(Point!U p) { return p.x >= 0 && p.x < cols && p.y >= 0 && p.y < rows; }
  pure auto points() const { return rows.to!U.iota.map!(y => cols.to!U.iota.map!(x => Point!U(x, y))).joiner; }
  pure auto sibPoints4(Point!U p) { return sibs4.map!(s => p + s).filter!(p => validPoint(p)); }
  pure auto sibPoints8(Point!U p) { return sibs8.map!(s => p + s).filter!(p => validPoint(p)); }
}

template Graph(Wt, Node, Wt _inf = 10 ^^ 9, Node _sent = Node.max)
{
  import std.algorithm, std.container, std.conv;

  const inf = _inf, sent = _sent;

  struct Edge { Node src, dst; Wt cap; }
  struct EdgeR { Node src, dst; Wt cap, flow; Node rev; }

  Wt fordFulkerson(Edge[][] g, Node s, Node t)
  {
    auto n = g.length;
    auto adj = withRev(g, n);

    auto visited = new bool[](n);

    Wt augment(Node u, Wt cur)
    {
      if (u == t) return cur;
      visited[u] = true;
      foreach (ref e; adj[u]) {
        if (!visited[e.dst] && e.cap > e.flow) {
          auto f = augment(e.dst, min(e.cap - e.flow, cur));
          if (f > 0) {
            e.flow += f;
            adj[e.dst][e.rev].flow -= f;
            return f;
          }
        }
      }
      return 0;
    }

    Wt flow;

    for (;;) {
      visited[] = false;
      auto f = augment(s, inf);
      if (f == 0) break;
      flow += f;
    }

    return flow;
  }

  EdgeR[][] withRev(Edge[][] g, size_t n)
  {
    auto r = new EdgeR[][](n);

    foreach (gi; g)
      foreach (e; gi) {
        r[e.src] ~= EdgeR(e.src, e.dst, e.cap, 0, cast(Node)(r[e.dst].length));
        r[e.dst] ~= EdgeR(e.dst, e.src, 0, 0, cast(Node)(r[e.src].length) - 1);
      }

    return r;
  }
}