#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define mk make_pair
#define pb push_back
#define alls(x) x.begin(), x.end()
#define sz(x) (int)(x.size())
#define forn(i, n) for (int i = 0; i < int(n); i++)
#define rep(i, n) for (int i = 1; i <= int(n); i++)
#define inc(i, l, r, d) for (int i = l; i <= r; i += d)
#define dec(i, r, l, d) for (int i = r; i >= l; i -= d)
#define dbg(x) cerr << #x << " = " << x << endl;
#define pii pair<int, int>
#define pll pair<ll, ll>
#define vi vector<int>
const ld eps = 1e-12;
const ll inf = 1e16;
const ll mod = 998244353;
const ll mod1 = 1e9 + 87;
const ll mod2 = 127397154761;
ll qpow(ll a, ll b) {if (b == 0) return 1; ll ans = qpow(a, b >> 1); ans = ans * ans % mod; if (b & 1) ans = ans * a % mod; return ans;}
using namespace std;
void IOS(string name = "") {
cin.tie(0);
cout.tie(0);
ios::sync_with_stdio(false);
if ((int)name.size()) {
freopen((name + ".in").c_str(), "r", stdin);
freopen((name + ".out").c_str(), "w", stdout);
}
}
const int maxn = 4005;
map<pii, vector<pair<pii, int>>> g;
int m, n;
char s[maxn][maxn];
int d[4][2] = {0, 1, 0, -1, 1, 0, -1, 0};
map<pii, int > dis;
map<pii, bool> vis;
bool check(int x1, int y1) {
return x1 > 0 && y1 > 0 && x1 <= m && y1 <= n;
}
void bfs() {
deque<pii> dq;
rep(i, m) {
rep(j, n) {
dis[mk(i, j)] = INT_MAX - 10;
}
}
dis[mk(1, 1)] = 1;
dq.pb(mk(1, 1));
vis[mk(1, 1)] = true;
while (!dq.empty()) {
pii u = dq.front(); dq.pop_front();
for (auto it: g[u]) {
pii v = it.first;
int w = it.second;
if (vis[v]) continue;
if (dis[v] > dis[u] + w) {
dis[v] = dis[u] + w;
vis[v] = true;
if (w == 1) {
dq.pb(v);
}
else {
dq.push_front(v);
}
}
}
}
}
int main() {
IOS();
cin >> m >> n;
rep(i, m) {
rep(j, n) {
cin >> s[i][j];
}
}
if (s[1][1] == '.') {
cout << 0 << endl;
return 0;
}
rep(i, m) {
rep(j, n) {
forn(k, 4) {
int x1 = i + d[k][0], y1 = j + d[k][1];
if (s[x1][y1] != '.' && check(x1, y1)) {
if (s[x1][y1] == s[i][j]) {
g[mk(i, j)].pb(mk(mk(x1, y1), 0));
}
else {
g[mk(i, j)].pb(mk(mk(x1, y1), 1));
}
}
}
}
}
bfs();
int ans = 0;
rep(i, m) {
rep(j, n) {
if (s[i][j] != '.') {
ans = max(ans, dis[mk(i, j)]);
}
}
}
cout << ans << endl;
return 0;
}
