#include <bits/stdc++.h>
using namespace std;
const int INF = INT_MAX / 2;
const int MAXN = 4000;
const int ox[] = {0, 1, 0, -1};
const int oy[] = {1, 0, -1, 0};
int n, m;
char mat[MAXN + 1][MAXN + 1];
int cost[MAXN + 1][MAXN + 1];
int main() {
cin >> n >> m;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> mat[i][j];
}
}
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cost[i][j] = INF;
}
}
deque<pair<int, int>> dq;
cost[0][0] = 1;
dq.push_front(make_pair(0, 0));
while (!dq.empty()) {
int x, y;
tie(x, y) = dq.front();
dq.pop_front();
for (int i = 0; i < 4; i++) {
int nx = x + ox[i];
int ny = y + oy[i];
if (nx < 0 || ny < 0 || nx == n || ny == m) {
continue;
}
if (mat[nx][ny] == '.') {
continue;
}
int t = 0;
if (mat[nx][ny] != mat[x][y]) {
t = 1;
}
if (cost[nx][ny] > cost[x][y] + t) {
cost[nx][ny] = t + cost[x][y];
if (t) {
dq.push_back(make_pair(nx, ny));
} else {
dq.push_front(make_pair(nx, ny));
}
}
}
}
int ans = -INF;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (mat[i][j] == '.') {
continue;
// cerr << "oo ";
}
// cerr << cost[i][j] << " ";
ans = max(ans, cost[i][j]);
}
// cerr << "\n";
}
cout << ans << "\n";
return 0;
}
