#include <iostream>
#include <vector>
#include <queue>
using namespace std;
struct heap {
int i, j, w;
bool operator < (const heap &o) const {
return w > o.w;
}
};
vector<pair<int, int>> dir = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
vector<string> grid(n);
for (auto &s:grid) cin >> s;
auto invalid = [&](int i, int j) -> bool {
return i < 0 || i >= n || j < 0 || j >= m || grid[i][j] == '.';
};
priority_queue<heap> pq;
vector<vector<int>> dist(n, vector<int>(m, 0));
vector<vector<bool>> vis(n, vector<bool>(m, false));
dist[0][0] = 1;
vis[0][0] = true;
pq.push({0, 0, 1});
int ans = 0;
while (!pq.empty()){
auto [i, j, W] = pq.top(); pq.pop();
ans = max(ans, dist[i][j]);
for (auto [di, dj]:dir){
if (invalid(i + di, j + dj) || vis[i + di][j + dj]) continue;
if (grid[i + di][j + dj] != grid[i][j]){
dist[i + di][j + dj] = dist[i][j] + 1;
vis[i + di][j + dj] = true;
pq.push({i + di, j + dj, dist[i][j] + 1});
}
else {
dist[i + di][j + dj] = dist[i][j];
vis[i + di][j + dj] = true;
pq.push({i + di, j + dj, dist[i][j]});
}
}
}
// for (int i = 0;i < n;i++){
// for (int j = 0;j < m;j++)
// cout << dist[i][j] << ' ';
// cout << '\n';
// }
cout << ans << '\n';
}
