#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream &operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const deque<T> &vec){ os << "deq["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream &operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream &operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream &operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> bool chmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool chmin(T &m, const T q) { if (q < m) {m = q; return true;} else return false; }
template<typename T1, typename T2> pair<T1, T2> operator+(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(const pair<T1, T2> &l, const pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
using namespace __gnu_pbds; // find_by_order(), order_of_key()
template<typename TK> using pbds_set = tree<TK, null_type, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename TK, typename TV> using pbds_map = tree<TK, TV, less<TK>, rb_tree_tag, tree_order_statistics_node_update>;
*/

vector<string> S;

constexpr std::array<int, 4> dx{1, -1, 0, 0};
constexpr std::array<int, 4> dy{0, 0, 1, -1};
struct GridGraph
{

    int H, W;

    GridGraph() = default;
    GridGraph(int h, int w) : H(h), W(w) {}

    /* Implement here. */
    using T_E = long long int;
    const T_E INF = 1e18;
    inline T_E edge_cost(int x_s, int y_s, int x_tt, int y_tt)
    {
        if (x_tt == x_s and y_tt == y_s + 1) {
            return S[x_s][y_s] != S[x_tt][y_tt];
        }
        if (x_tt == x_s + 1 and y_tt == y_s) {
            return S[x_s][y_s] != S[x_tt][y_tt];
        }
        return 1e9;
    }

    // Dijkstra's algorithm
    // Complexity: O(HWlog(HW))
    std::vector<std::vector<T_E>> dij; // Distance from (x_s, y_s)
    std::vector<std::vector<std::pair<int, int>>> dij_prv; // Previous node for Dijkstra optimal path
    void dijkstra(int x_s, int y_s) {
        dij.assign(H, std::vector<T_E>(W, INF));
        dij_prv.assign(H, std::vector<std::pair<int, int>>(W, std::make_pair(-1, -1)));

        using P = std::tuple<T_E, int, int>;
        std::priority_queue<P, std::vector<P>, std::greater<P>> pq;
        dij[x_s][y_s] = 0;
        pq.emplace(0, x_s, y_s);
        while (!pq.empty()) {
            T_E dnow;
            int x, y;
            std::tie(dnow, x, y) = pq.top();
            pq.pop();
            if (dij[x][y] < dnow) continue;
            for (size_t d = 0; d < dx.size(); d++) {
                int xn = x + dx[d], yn = y + dy[d];
                if (xn < 0 or yn < 0 or xn >= H or yn >= W) continue;
                T_E dnxt = dnow + edge_cost(x, y, xn, yn);
                if (dnxt < dij[xn][yn]) {
                    dij[xn][yn] = dnxt;
                    dij_prv[xn][yn] = std::make_pair(x, y);
                    pq.emplace(dnxt, xn, yn);
                }
            }
        }
    }
};

int main()
{
    int H, W;
    cin >> H >> W;
    S.resize(H);
    cin >> S;
    GridGraph graph(H, W);
    int ret = 0;
    if (S[0][0] == '#' and S.back().back() == '#') ret++;
    graph.dijkstra(0, 0);
    cout << ret + (graph.dij[H - 1][W - 1] + 1) / 2 << endl;
}


Measured memory_bytes: 512