#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
using ll = long long;
using ld = long double;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define sz(x) (int)x.size()
//#define endl '\n'
const int mod = 1e9 + 7;
const int inf = 2e9 + 5;
const ll linf = 9e18 + 5;
int n, m;
const int N = 4e3 + 5;
char c[N][N];
int dist[N][N];
void init() {
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
c[i][j] = '.';
}
}
}
void input() {
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> c[i][j];
}
}
}
void bfs() {
deque<pair<int, int>> dq;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
dist[i][j] = inf;
}
}
dist[1][1] = 1;
dq.push_back(mp(1, 1));
while (!dq.empty()) {
int x = dq.front().fi;
int y = dq.front().se;
dq.pop_front();
for (int dx = -1; dx <= 1; dx++) {
for (int dy = -1; dy <= 1; dy++) {
if (abs(dx) + abs(dy) != 1) {
continue;
}
if (dist[x + dx][y + dy] != inf) {
continue;
}
if (c[x + dx][y + dy] == '.') {
continue;
}
if (c[x + dx][y + dy] != c[x][y] && dist[x + dx][y + dy] > dist[x][y] + 1) {
dist[x + dx][y + dy] = dist[x][y] + 1;
dq.push_back(mp(x + dx, y + dy));
}
else if (dist[x + dx][y + dy] > dist[x][y]) {
dist[x + dx][y + dy] = dist[x][y];
dq.push_front(mp(x + dx, y + dy));
}
}
}
}
}
void solve() {
bfs();
int ans = 0;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (dist[i][j] != inf) {
ans = max(ans, dist[i][j]);
}
}
}
cout << ans;
}
void output() {
}
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int number_of_testcases = 1;
//cin >> number_of_testcases;
while (number_of_testcases--) {
init();
input();
solve();
output();
}
return 0;
}
