#include <bits/stdc++.h>
using namespace std;

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

    int H, W;
    cin >> H >> W;
    vector<string> C(H);
    for (auto &s : C) cin >> s;

    const int INF = 1e9;
    int HH = 2 * H - 1, WW = 2 * W - 1;
    vector<int> a(WW, INF), b(WW, INF), c(WW);

    for (int i = 0; i < HH; i++) {
        fill(c.begin(), c.end(), INF);
        for (int j = 0; j < WW; j++) {
            if (i % 2 == 0 && j % 2 == 0 && C[i / 2][j / 2] == '#') continue;

            int v = i || j ? INF : 0;
            if (i) v = min(v, b[j] + 1);
            if (j) v = min(v, c[j - 1] + 1);
            if (i >= 2 && i % 2 == 0) v = min(v, a[j] + 1);
            if (j >= 2 && j % 2 == 0) v = min(v, c[j - 2] + 1);

            c[j] = v;
        }
        a.swap(b);
        b.swap(c);
    }

    cout << b.back() << '\n';
}