#include <algorithm>
#include <array>
#include <cassert>
#include <deque>
#include <functional>
#include <iostream>
#include <cstring>
#include <ctime>
#include <chrono>
#include <numeric>
#include <queue>
#include <set>
#include <vector>
#include <random>
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
#define all(x) (x).begin(), (x).end()
#define isz(x) (int)(x.size())
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
const int sz = 4200, inf = 1000000000;
const ll mod = 1000000007, INF = 1000000000000000000;
char a[sz][sz];
int d[sz][sz];
int n, m;
void djk() {
deque<array<int, 2>> pq;
pq.push_front({1, 1});
d[1][1] = 1;
while (!pq.empty()) {
auto [i, j] = pq.front();
pq.pop_front();
if (j + 1 <= m && a[i][j+1] != '.' && d[i][j+1] > d[i][j] + (a[i][j] != a[i][j+1])) {
d[i][j+1] = d[i][j] + (a[i][j] != a[i][j+1]);
if (a[i][j] == a[i][j+1])
pq.push_front({i, j+1});
else
pq.push_back({i, j+1});
}
if (j >= 2 && a[i][j-1] != '.' && d[i][j-1] > d[i][j] + (a[i][j] != a[i][j-1])) {
d[i][j-1] = d[i][j] + (a[i][j] != a[i][j-1]);
if (a[i][j] == a[i][j-1]) pq.push_front({i, j-1});
else pq.push_back({i, j-1});
}
if (i + 1 <= n && a[i+1][j] != '.' && d[i+1][j] > d[i][j] + (a[i][j] != a[i+1][j])) {
d[i+1][j] = d[i][j] + (a[i][j] != a[i+1][j]);
if (a[i][j] == a[i+1][j]) pq.push_front({i+1, j});
else pq.push_back({i+1, j});
}
if (i >= 2 && a[i-1][j] != '.' && d[i-1][j] > d[i][j] + (a[i][j] != a[i-1][j])) {
d[i-1][j] = d[i][j] + (a[i][j] != a[i-1][j]);
if (a[i][j] == a[i-1][j]) pq.push_front({i-1, j});
else pq.push_back({i-1, j});
}
}
}
void solve() {
cin >> n >> m;
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++) {
cin >> a[i][j];
}
}
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++) {
d[i][j] = inf;
}
}
djk();
int mx = 0;
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++) {
mx = max(mx, (d[i][j] != inf ? d[i][j] : -1));
}
}
cout << mx << '\n';
}
void precompute() {}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
#ifdef LOCAL
// freopen("err.log", "w", stderr);
// freopen("in.txt", "r", stdin);
#endif
precompute();
solve();
}
