#include <bits/stdc++.h>

using namespace std;

constexpr int N = 64;

bool b[N][N];
int c[N][N], d[N][N], p[N * N], h, w;

int chk(int i, int j) { return i >= 0 && j >= 0 && i <= h && j <= w; }
int get(int i, int j) { return chk(i, j) && b[i][j]; }
int getp(int v) { return p[v] == v? v: p[v] = getp(p[v]); }
void uni(int u, int v) { p[getp(v)] = getp(u); }

int main() {
  cin.tie(0)->sync_with_stdio(0);
  cin >> h >> w;
  for (int i = 0; i < h; ++i) if (string s; cin >> s, 1)
  for (int j = 0; j < w; ++j) b[i][j] = s[j] == '#';
  fill(d[0] + 1, d[N], 1e9);
  iota(p, end(p), 0);
  for (int i = 0; i <= h; ++i)
  for (int j = 0; j <= w; ++j)
  for (auto di: {-1, 0})
  for (auto dj: {-1, 0}) c[i][j] += get(i + di, j + dj);
  for (int i = 0; i <= h; ++i)
  for (int j = 0; j <= w; ++j) if (!c[i][j]) {
    if (i && !c[i - 1][j]) uni(i * N + j, i * N + j - N);
    if (j && !c[i][j - 1]) uni(i * N + j, i * N + j - 1);
  }
  priority_queue pq{greater{}, vector<int>{{}}};
  array<int, 4> ta[2];
  while (pq.size()) {
    auto t = pq.top(); pq.pop();
    int cd = t >> 12, i = t >> 6 & 63, j = t & 63;
    if (cd != d[i][j]) continue;
    for (auto di: {-1, 0, 1})
    for (auto dj: {-1, 0, 1}) if (!chk(i + di, j + dj)); else if (!di ^ !dj)
    if (auto t = cd + get(i + di - (di < 1), j + dj - (dj < 1)) + get(i + di - (di < 0), j + dj - (dj < 0)); d[i + di][j + dj] > t) {
      pq.push((d[i + di][j + dj] = t) << 12 | i + di << 6 | j + dj);
    } else; else if (di && d[i + di][j + dj] > cd + c[i + di][j + dj] - b[i][j]) {
      ta[0] = ta[1] = {-1, -1, -1, -1};
      for (int w: {0, 1}) if (int p = 0; 1)
      for (int ddi: {0, 1, 2})
      for (int ddj: {0, 1, 2}) if ((ddi == 2) ^ (ddj == 2)) if (int ni = i + di * (w? ddi + 1: -ddi), nj = j + dj * (w? ddj + 1: -ddj); chk(ni, nj) && !c[ni][nj]) {
        ta[w][p++] = getp(ni * N + nj);
      }
      bool ok = 0;
      for (auto& a: ta[0]) if (~a)
      for (auto& b: ta[1]) ok |= a == b;
      if (ok) pq.push((d[i + di][j + dj] = cd + c[i + di][j + dj] - b[i][j]) << 12 | i + di << 6 | j + dj);
    }
  }
  cout << d[h][w] + b[0][0];
}