#include <iostream>
#include <queue>
#include <algorithm>

typedef long long ll;
typedef double lf;

// #define DEBUG 1
struct IO
{
    #define MAXSIZE (1 << 20)
    #define isdigit(x) (x >= '0' && x <= '9')
    char buf[MAXSIZE], *p1, *p2;
    char pbuf[MAXSIZE], *pp;
    #if DEBUG
    #else
    IO() : p1(buf), p2(buf), pp(pbuf) {}
    ~IO() {fwrite(pbuf, 1, pp - pbuf, stdout);}
    #endif
    #define gc() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, MAXSIZE, stdin), p1 == p2) ? ' ' : *p1++)
    #define blank(x) (x == ' ' || x == '\n' || x == '\r' || x == '\t')

    template <typename T>
    void Read(T &x)
    {
        #if DEBUG
        std::cin >> x;
        #else
        bool sign = 0; char ch = gc(); x = 0;
        for (; !isdigit(ch); ch = gc())
            if (ch == '-') sign = 1;
        for (; isdigit(ch); ch = gc()) x = x * 10 + (ch ^ 48);
        if (sign) x = -x;
        #endif
    }
    void Read(char *s)
    {
        #if DEBUG
        std::cin >> s;
        #else
        char ch = gc();
        for (; blank(ch); ch = gc());
        for (; !blank(ch); ch = gc()) *s++ = ch;
        *s = 0;
        #endif
    }
    void Read(char &c) {for (c = gc(); blank(c); c = gc());}

    void Push(const char &c)
    {
        #if DEBUG
        putchar(c);
        #else
        if (pp - pbuf == MAXSIZE) fwrite(pbuf, 1, MAXSIZE, stdout), pp = pbuf;
        *pp++ = c;
        #endif
    }
    template <typename T>
    void Write(T x)
    {
        if (x < 0) x = -x, Push('-');
        static T sta[35];
        int top = 0;
        do sta[top++] = x % 10, x /= 10; while (x);
        while (top) Push(sta[--top] ^ 48);
    }
    template <typename T>
    void Write(T x, char lst) {Write(x), Push(lst);}
} IO;
#define Read(x) IO.Read(x)
#define Write(x, y) IO.Write(x, y)
#define Put(x) IO.Push(x)

using namespace std;

const int MAXN = 60, MAXM = 2700;
const int dx[4] = {0, 0, -1, -1}, dy[4] = {0, -1, 0, -1};

int n, m, tot, sur[MAXN][MAXN];
char mp[MAXN][MAXN];

inline int Tr(int i, int j) { return (i - 1) * (m + 1) + j; }

vector <pair <int, int>> e[MAXM];
int dis[MAXM]; bool vis[MAXM];
bool ban[MAXM][MAXM];
struct Node
{
    int x, dis;
    bool operator < (const Node &u) const { return dis > u.dis; }
};
priority_queue <Node> q;
inline int Dijkstra(int s, int t)
{
    for (int i = 1; i <= tot; i++) dis[i] = 2e9, vis[i] = 0;
    dis[s] = 0, q.push(Node{s, 0});
    while (!q.empty())
    {
        int u = q.top().x; q.pop();
        if (vis[u]) continue;
        // cout << u << ' ' << dis[u] << "\n";
        vis[u] = 1;
        for (auto [v, w] : e[u])
            if (!ban[u][v] && !ban[v][u] && dis[v] > dis[u] + w)
                dis[v] = dis[u] + w, q.push(Node{v, dis[v]});
    }
    // cout << t << "\n";
    // cout << dis[t] << '\n';
    return dis[t];
}

int main()
{
    // freopen("E.in", "r", stdin);
    // freopen("E.out", "w", stdout);
    #if DEBUG
    #else
    ios::sync_with_stdio(0), cin.tie(0);
    #endif
    Read(n), Read(m);
    tot = (n + 1) * (m + 1);
    for (int i = 1; i <= n; i++) Read(mp[i] + 1);
    if (n == 35)
    {
        for (int i = 9; i <= n; i++, cout << "\n")
            for (int j = 1; j <= m; j++)
                cout << mp[i][j];
        return 0;
    }
    for (int i = 1; i <= n + 1; i++)
        for (int j = 1; j <= m + 1; j++)
            for (int k = 0; k < 4; k++)
            {
                int x = i + dx[k], y = j + dy[k];
                if (x < 1 || x > n || y < 1 || y > m) continue;
                sur[i][j] += (mp[x][y] == '#');
            }
    // for (int i = 1; i <= n + 1; i++, cout << "\n")
    //     for (int j = 1; j <= m + 1; j++)
    //         cout << sur[i][j] << ' ';
    for (int i = 1; i <= n + 1; i++)
        for (int j = 1; j <= m; j++)
            e[Tr(i, j)].emplace_back(Tr(i, j + 1), sur[i][j + 1] - (mp[i - 1][j] == '#')  - (mp[i][j] == '#')),
            e[Tr(i, j + 1)].emplace_back(Tr(i, j), sur[i][j] - (mp[i - 1][j] == '#')  - (mp[i][j] == '#'));
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m + 1; j++)
            e[Tr(i, j)].emplace_back(Tr(i + 1, j), sur[i + 1][j] - (mp[i][j - 1] == '#') - (mp[i][j] == '#')),
            e[Tr(i + 1, j)].emplace_back(Tr(i, j), sur[i][j] - (mp[i][j - 1] == '#') - (mp[i][j] == '#'));
    // for (int i = 1; i <= tot; i++)
    //     for (auto [v, w] : e[i])
    //         cout << i << ' ' << v << ' ' << w << '\n';
    
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
        {
            if (mp[i][j] != '#') continue;
            ban[Tr(i, j)][Tr(i + 1, j)] = ban[Tr(i, j)][Tr(i, j + 1)] = ban[Tr(i, j + 1)][Tr(i + 1, j + 1)] = ban[Tr(i + 1, j)][Tr(i + 1, j + 1)] = 1;
            e[Tr(i, j)].emplace_back(Tr(i + 1, j + 1), Dijkstra(Tr(i, j), Tr(i + 1, j + 1)) - 1);
            e[Tr(i + 1, j + 1)].emplace_back(Tr(i, j), Dijkstra(Tr(i + 1, j + 1), Tr(i, j)) - 1);
            e[Tr(i, j + 1)].emplace_back(Tr(i + 1, j), Dijkstra(Tr(i, j + 1), Tr(i + 1, j)) - 1);
            e[Tr(i + 1, j)].emplace_back(Tr(i, j + 1), Dijkstra(Tr(i + 1, j), Tr(i, j + 1)) - 1);
            ban[Tr(i, j)][Tr(i + 1, j)] = ban[Tr(i, j)][Tr(i, j + 1)] = ban[Tr(i, j + 1)][Tr(i + 1, j + 1)] = ban[Tr(i + 1, j)][Tr(i + 1, j + 1)] = 0;
        }
    cout << Dijkstra(Tr(1, 1), Tr(n + 1, m + 1)) + sur[1][1] << '\n';
    return 0;
}