#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

#define pb push_back
#define sz(x) (int)x.size()
#define all(x) begin(x),end(x)
#define lb(x,y) lower_bound(all(x),y)-begin(x)

mt19937 rng;

void solve() {
	int N, M; cin >> N >> M;
	vector<string> mat(N);
	for (int i = 0; i < N; i++) cin >> mat[i];
	vector<vector<int>> dist(N + 1, vector<int>(M + 1, INT_MAX));
	dist[0][0] = mat[0][0] == '#';
	priority_queue<pair<int, pair<int, int>>> pq;
	pq.push({0, {0, 0}});
	vector<vector<bool>> vis(N + 1, vector<bool>(M + 1, 0));
	vector<int> x = {0, 1, 0, -1}, y = {1, 0, -1, 0};
	while (!pq.empty()) {
		int r = pq.top().second.first, c = pq.top().second.second; pq.pop();
		if (vis[r][c]) continue;
		vis[r][c] = 1;
		set<pair<int, int>> s1;
		for (int i = -1; i <= 0; i++) {
			for (int j = -1; j <= 0; j++) {
				if (r + i >= 0 && r + i < N && c + j >= 0 && c + j < M) s1.insert({r + i, c + j});
			}
		}
		for (int k = 0; k < 4; k++) {
			int r2 = r + x[k], c2 = c + y[k];
			if (r2 >= 0 && r2 <= N && c2 >= 0 && c2 <= M) {
				set<pair<int, int>> s2;
				for (int i = -1; i <= 0; i++) {
					for (int j = -1; j <= 0; j++) {
						if (r2 + i >= 0 && r2 + i < N && c2 + j >= 0 && c2 + j < M) s2.insert({r2 + i, c2 + j});
					}
				}
				int cnt = 0;
				for (auto &p : s2) {
					if (!s1.count(p) && mat[p.first][p.second] == '#') cnt++;
				}
				if (dist[r][c] + cnt < dist[r2][c2]) {
					dist[r2][c2] = dist[r][c] + cnt;
					pq.push({-dist[r2][c2], {r2, c2}});
				}
			}
		}
		for (int dx = -1; dx <= 1; dx += 2) {
			for (int dy = -1; dy <= 1; dy += 2) {
				int r2 = r + dx, c2 = c + dy;
				if (r2 >= 0 && r2 <= N && c2 >= 0 && c2 <= M) {
					set<pair<int, int>> skip;
					for (int i = -1; i <= 0; i++) {
						for (int j = -1; j <= 0; j++) {
							if (r + i >= 0 && r + i < N && c + j >= 0 && c + j < M) {
								skip.insert({r + i, c + j});
							}
							if (r2 + i >= 0 && r2 + i < N && c2 + j >= 0 && c2 + j < M) {
								skip.insert({r2 + i, c2 + j});
							}
						}
					}
					vector<vector<bool>> vis2(N + 1, vector<bool>(M + 1, 0));
					vis2[r][c] = 1;
					queue<pair<int, int>> q;
					q.push({r, c});
					while (!q.empty()) {
						int r3 = q.front().first, c3 = q.front().second; q.pop();
						for (int k = 0; k < 4; k++) {
							int r4 = r3 + x[k], c4 = c3 + y[k];
							if (r4 >= 0 && r4 <= N && c4 >= 0 && c4 <= M) {
								bool bad = 0;
								for (int i = -1; i <= 0; i++) {
									for (int j = -1; j <= 0; j++) {
										if (r4 + i >= 0 && r4 + i < N && c4 + j >= 0 && c4 + j < M && mat[r4 + i][c4 + j] == '#' && !skip.count({r4 + i, c4 + j})) {
											bad = 1;
										}
									}
								}
								if (!bad && !vis2[r4][c4]) {
									vis2[r4][c4] = 1;
									q.push({r4, c4});
								}
							}
						}
					}
					if (vis2[r2][c2]) {
						set<pair<int, int>> s2;
						for (int i = -1; i <= 0; i++) {
							for (int j = -1; j <= 0; j++) {
								if (r2 + i >= 0 && r2 + i < N && c2 + j >= 0 && c2 + j < M) s2.insert({r2 + i, c2 + j});
							}
						}
						int cnt = 0;
						for (auto &p : s2) {
							if (!s1.count(p) && mat[p.first][p.second] == '#') cnt++;
						}
						if (dist[r][c] + cnt < dist[r2][c2]) {
							dist[r2][c2] = dist[r][c] + cnt;
							pq.push({-dist[r2][c2], {r2, c2}});
						}
					}
				}
			}
		}
	}
	cout << dist[N][M] << "\n";
}

int main() {
	ios::sync_with_stdio(false);
    cin.tie(nullptr);
    rng = mt19937(chrono::steady_clock::now().time_since_epoch().count());

    solve();

    return 0;
}