#include <bits/stdc++.h>
#define INF_INT 2147483647
#define what_is(x) cerr << #x << " is " << x << endl;
#define all(v) v.begin(), v.end()
typedef long long ll;
using namespace std;
void solve() {
int H, W; cin >> H >> W;
string grid[H];
for (auto &el: grid) cin >> el;
vector<vector<int>> dist(H, vector<int>(W, 1e9));
deque<pair<int, int>> dq;
dq.push_back({0, 0});
dist[0][0] = 0;
while (!dq.empty()) {
pair<int, int> current = dq.front();
dq.pop_front();
// go down
if (current.first + 1 < H && (grid[current.first + 1][current.second] != '.')) {
if (grid[current.first + 1][current.second] != grid[current.first][current.second]) {
if (dist[current.first + 1][current.second] > dist[current.first][current.second] + 1) {
dist[current.first + 1][current.second] = dist[current.first][current.second] + 1;
dq.push_back({current.first + 1, current.second});
}
} else {
if (dist[current.first + 1][current.second] > dist[current.first][current.second]) {
dist[current.first + 1][current.second] = dist[current.first][current.second];
dq.push_front({current.first + 1, current.second});
}
}
}
// go left
// cout << "UP" << endl;
if (current.second - 1 >= 0 && grid[current.first][current.second - 1] != '.') {
if (grid[current.first][current.second - 1] != grid[current.first][current.second]) {
if (dist[current.first][current.second - 1] > dist[current.first][current.second] + 1) {
dist[current.first][current.second - 1] = dist[current.first][current.second] + 1;
dq.push_back({current.first, current.second - 1});
}
} else {
if (dist[current.first][current.second - 1] > dist[current.first][current.second]) {
dist[current.first][current.second - 1] = dist[current.first][current.second];
dq.push_front({current.first, current.second - 1});
}
}
}
// go right
if (current.second + 1 < W && grid[current.first][current.second + 1] != '.') {
if (grid[current.first][current.second + 1] != grid[current.first][current.second]) {
if (dist[current.first][current.second + 1] > dist[current.first][current.second] + 1) {
dist[current.first][current.second + 1] = dist[current.first][current.second] + 1;
dq.push_back({current.first, current.second + 1});
}
} else {
if (dist[current.first][current.second + 1] > dist[current.first][current.second]) {
dist[current.first][current.second + 1] = dist[current.first][current.second];
dq.push_front({current.first, current.second + 1});
}
}
}
// go up
if (current.first - 1 >= 0 && grid[current.first - 1][current.second] != '.') {
if (grid[current.first - 1][current.second] != grid[current.first][current.second]) {
if (dist[current.first - 1][current.second] > dist[current.first][current.second] + 1) {
dist[current.first - 1][current.second] = dist[current.first][current.second] + 1;
dq.push_back({current.first - 1, current.second});
}
} else {
if (dist[current.first - 1][current.second] > dist[current.first][current.second]) {
dist[current.first - 1][current.second] = dist[current.first][current.second];
dq.push_front({current.first - 1, current.second});
}
}
}
}
int ans = -1;
for (int i = 0; i < H; i++) {
for (int j = 0; j < W; j++) {
if (dist[i][j] != (int) 1e9) ans = max(ans, dist[i][j]);
}
}
cout << ans + 1 << '\n';
}
int main(void) {
ios::sync_with_stdio(false);
cin.tie(nullptr);
solve();
return 0;
}
