#include "bits/stdc++.h"

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rep(i, n) for (intmax_t i = 0, i##_limit = (n); i < i##_limit; ++i)
#define reps(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__)

constexpr size_t    operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t  operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

template <class T, class Compare = less<>>
using MaxHeap = priority_queue<T, vector<T>, Compare>;
template <class T, class Compare = greater<>>
using MinHeap = priority_queue<T, vector<T>, Compare>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head&& head, Tail&&... tail) {
    cin >> head;
    input(forward<Tail>(tail)...);
}

template <class T>
inline istream& operator>>(istream &is, vector<T> &vec) {
    for (auto &e: vec) {
        is >> e;
    }
    return is;
}

inline void output() { cout << "\n"; }
template <class Head, class... Tail>
inline void output(Head&& head, Tail&&... tail) {
    cout << head;
    if (sizeof...(tail)) {
        cout << " ";
    }
    output(forward<Tail>(tail)...);
}

template <class T>
inline ostream& operator<<(ostream &os, const vector<T> &vec) {
    static constexpr const char *delim[] = {" ", ""};
    for (const auto &e: vec) {
        os << e << delim[&e == &vec.back()];
    }
    return os;
}

template <class T>
inline vector<T> makeVector(const T &initValue, size_t sz) {
    return vector<T>(sz, initValue);
}

template <class T, class... Args>
inline auto makeVector(const T &initValue, size_t sz, Args... args) {
    return vector<decltype(makeVector<T>(initValue, args...))>(sz, makeVector<T>(initValue, args...));
}

template <class Func>
class FixPoint : Func {
public:
    explicit constexpr FixPoint(Func&& f) noexcept : Func(forward<Func>(f)) {}

    template <class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const {
        return Func::operator()(*this, std::forward<Args>(args)...);
    }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept {
    return FixPoint<Func>{forward<Func>(f)};
}

template <class T>
inline bool chmax(T &a, const T &b) noexcept {
    return b > a && (a = b, true);
}

template <class T>
inline bool chmin(T &a, const T &b) noexcept {
    return b < a && (a = b, true);
}

template <class T>
inline T diff(const T &a, const T &b) noexcept {
    return a < b ? b - a : a - b;
}
// End Header }}}

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

    var(size_t, H, W);

    vector<string> s(H);
    input(s);

    int res = INF;
    {
        auto dp = makeVector<int>(INF, H, W);
        dp[0][0] = (s[0][0] != '.');

        reps(j, 1, W - 1) {
            chmin(dp[0][j], dp[0][j - 1] + (s[0][j - 1] == '.' && s[0][j] == '#'));
        }
        reps(i, 1, H - 1) {
            chmin(dp[i][0], dp[i - 1][0] + (s[i - 1][0] == '.' && s[i][0] == '#'));
        }

        reps(i, 1, H - 1) reps(j, 1, W - 1) {
            chmin(dp[i][j], dp[i - 1][j] + (s[i - 1][j] == '.' && s[i][j] == '#'));
            chmin(dp[i][j], dp[i][j - 1] + (s[i][j - 1] == '.' && s[i][j] == '#'));
        }

        chmin(res, dp[H - 1][W - 1]);
    }

    {
        auto dp = makeVector<int>(INF, H, W);
        dp[0][0] = (s[0][0] != '#');

        reps(j, 1, W - 1) {
            chmin(dp[0][j], dp[0][j - 1] + (s[0][j - 1] == '#' && s[0][j] == '.'));
        }
        reps(i, 1, H - 1) {
            chmin(dp[i][0], dp[i - 1][0] + (s[i - 1][0] == '#' && s[i][0] == '.'));
        }

        reps(i, 1, H - 1) reps(j, 1, W - 1) {
            chmin(dp[i][j], dp[i - 1][j] + (s[i - 1][j] == '#' && s[i][j] == '.'));
            chmin(dp[i][j], dp[i][j - 1] + (s[i][j - 1] == '#' && s[i][j] == '.'));
        }

        chmin(res, dp[H - 1][W - 1] + (s[H - 1][W - 1] == '#'));
    }

    output(res);

    return 0;
}


Measured memory_bytes: 384