#include <bits/stdc++.h>
using namespace std;
#define int long long int
void solve() {
int n, m, ans = 0;
cin >> n >> m;
vector<string> grid(n);
vector<vector<int>> dist(n, vector<int>(m, 0));
for (string &x : grid) {
cin >> x;
}
deque<pair<int, int>> q;
dist[0][0] = 1;
q.push_back({0, 0});
while(!q.empty()) {
auto [i, j] = q.front();
q.pop_front();
if (i+1 < n && !dist[i+1][j] && grid[i+1][j] != '.') {
dist[i+1][j] = dist[i][j];
if (grid[i][j] != grid[i+1][j]) {
dist[i+1][j]++;
q.push_back({i+1, j});
} else {
q.push_front({i+1, j});
}
}
if (j+1 < m && !dist[i][j+1] && grid[i][j+1] != '.') {
dist[i][j+1] = dist[i][j];
if (grid[i][j] != grid[i][j+1]) {
dist[i][j+1]++;
q.push_back({i, j+1});
} else {
q.push_front({i, j+1});
}
}
if (i-1 >= 0 && !dist[i-1][j] && grid[i-1][j] != '.') {
dist[i-1][j] = dist[i][j];
if (grid[i][j] != grid[i-1][j]) {
dist[i-1][j]++;
q.push_back({i-1, j});
} else {
q.push_front({i-1, j});
}
}
if (j-1 >= 0 && !dist[i][j-1] && grid[i][j-1] != '.') {
dist[i][j-1] = dist[i][j];
if (grid[i][j] != grid[i][j-1]) {
dist[i][j-1]++;
q.push_back({i, j-1});
} else {
q.push_front({i, j-1});
}
}
}
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
ans = max(ans, dist[i][j]);
}
}
cout << ans << endl;
}
int32_t main() {
ios::sync_with_stdio(0);
cin.tie(0);
int t;
t = 1;
while(t--) {
solve();
}
}
