#pragma GCC optimize("O3", "unroll-loops")

#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <bitset>
#include <sstream>
#include <deque>
#include <queue>
#include <complex>
#include <random>
#include <cassert>
#include <chrono>

using namespace std;

#define FAST ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define FIXED cout << fixed << setprecision(12)
#define ll long long
#define ld long double
#define pii pair<int, int>
#define pll pair<ll, ll>
#define graph vector<vector<int>>
#define pb push_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define f first
#define s second
#define hashmap unordered_map
#define hashset unordered_set
#define eps 1e-9
#define mod 1000000007
#define inf 3000000000000000007ll
#define sz(a) signed(a.size())
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()

#ifdef DEBUG
    mt19937 gen(857204);
#else
    mt19937 gen(chrono::high_resolution_clock::now().time_since_epoch().count());
#endif

template<class T, class U> inline void checkmin(T &x, U y) { if (y < x) x = y; }
template<class T, class U> inline void checkmax(T &x, U y) { if (y > x) x = y; }
template<class T, class U> inline bool ifmax(T &x, U y) { if (y > x) return x = y, true; return false; }
template<class T, class U> inline bool ifmin(T &x, U y) { if (y < x) return x = y, true; return false; }
template<class T> inline void sort(T &a) { sort(all(a)); }
template<class T> inline void rsort(T &a) { sort(rall(a)); }
template<class T> inline void reverse(T &a) { reverse(all(a)); }
template<class T, class U> inline istream& operator>>(istream& str, pair<T, U> &p) { return str >> p.f >> p.s; }
template<class T> inline istream& operator>>(istream& str, vector<T> &a) { for (auto &i : a) str >> i; return str; }
template<class T> inline T sorted(T a) { sort(a); return a; }

signed main() {
    FAST; FIXED;
    int n, m;
    cin >> n >> m;
    vector<string> a(n);
    cin >> a;
    vector<vector<vector<pair<int, pii>>>> go(n, vector<vector<pair<int, pii>>>(m));
    for (int i = 0; i < n; ++i)
        for (int j = 0; j < m; ++j) {
            if (a[i][j] == '.') {
                if (i < n - 1) {
                    if (a[i + 1][j] == '#') {
                        go[i][j].pb({1, {i + 1, j}});
                    } else {
                        go[i][j].pb({0, {i + 1, j}});
                    }
                }
                if (j < m - 1) {
                    if (a[i][j + 1] == '#') {
                        go[i][j].pb({1, {i, j + 1}});
                    } else {
                        go[i][j].pb({0, {i, j + 1}});
                    }
                }
            } else {
                if (i < n - 1) go[i][j].pb({0, {i + 1, j}});
                if (j < m - 1) go[i][j].pb({0, {i, j + 1}});
            }
        }
    for (auto &i : go)
        for (auto &j : i)
            sort(j);
    deque<pii> que;
    que.pb({0, 0});
    vector<vector<int>> dist(n, vector<int>(m, mod));
    dist[0][0] = 0;
    while (sz(que)) {
        auto f = que.front();
        que.popf();
        for (auto i : go[f.f][f.s])
            if (ifmin(dist[i.s.f][i.s.s], dist[f.f][f.s] + i.f)) {
                if (i.f == 0) que.push_front(i.s);
                else que.push_back(i.s);
            }
    }
    cout << dist[n - 1][m - 1] + (a[0][0] == '#');
    #ifdef DEBUG
        cerr << "Runtime is: " << clock() * 1.0 / CLOCKS_PER_SEC << endl;
    #endif
    return 0;
}

Measured memory_bytes: 896