#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<unordered_map>
#include<unordered_set>
using namespace std;
using ll = long long;
ll mod = 1e9 + 7;
ll gcd(ll a, ll b) {
if (b == 0)return a;
else return gcd(b, a % b);
}
void solve() {
int n, m; cin >> n >> m;
vector<string>v(n);
for (int i = 0; i < n; i++) {
cin >> v[i];
}
if (v[0][0] == '.') {
cout << 0 << endl;
return;
}
priority_queue<pair<int, pair<int, int>>>q;
vector<vector<int>>dist(n, vector<int>(m, 1e9));
q.push({ -1,{0,0} });
dist[0][0] = 1;
while (q.size()) {
int i = q.top().second.first, j = q.top().second.second, qash = -q.top().first;
q.pop();
if (i + 1 < n) {
if (v[i + 1][j] != '.') {
if (v[i + 1][j] == v[i][j]) {
if (qash < dist[i + 1][j]) {
dist[i + 1][j] = qash;
q.push({ -qash,{i + 1,j} });
}
}
else {
qash++;
if (qash < dist[i + 1][j]) {
dist[i + 1][j] = qash;
q.push({ -qash,{i + 1,j} });
}
qash--;
}
}
}
if (j + 1 < m) {
if (v[i][j + 1] != '.') {
if (v[i][j + 1] == v[i][j]) {
if (qash < dist[i][j + 1]) {
dist[i][j+1] = qash;
q.push({ -qash,{i,j + 1} });
}
}
else {
qash++;
if (qash < dist[i][j + 1]) {
dist[i][j + 1] = qash;
q.push({ -qash,{i,j + 1} });
}
qash--;
}
}
}
if (i - 1 >= 0) {
if (v[i - 1][j] != '.') {
if (v[i - 1][j] == v[i][j]) {
if (qash < dist[i - 1][j]) {
dist[i - 1][j] = qash;
q.push({ -qash,{i - 1,j} });
}
}
else {
qash++;
if (qash < dist[i - 1][j]) {
dist[i - 1][j] = qash;
q.push({ -qash,{i - 1,j} });
}
qash--;
}
}
}
if (j - 1 >= 0) {
if (v[i][j - 1] != '.') {
if (v[i][j - 1] == v[i][j]) {
if (qash < dist[i][j - 1]) {
dist[i][j - 1] = qash;
q.push({ -qash,{i,j - 1} });
}
}
else {
qash++;
if (qash < dist[i][j - 1]) {
dist[i][j - 1] = qash;
q.push({ -qash,{i,j - 1} });
}
qash--;
}
}
}
}
int mx = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
//cout << min(dist[i][j], 9) << " ";
if (v[i][j] != '.') {
mx = max(mx, dist[i][j]);
}
}
//cout << endl;
}
cout << mx << endl;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(nullptr);
cout.tie(nullptr);
ll t = 1;
//cin >> t;
while (t--) {
solve();
}
}
