#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fll;
int n, m;
vector<string> g;
int X[4] = {0, -1, 1, 0};
int Y[4] = {-1, 0, 0, 1};
bool is_Valid(int x, int y){
return (x >= 0 && x < n && y >= 0 && y < m && g[x][y] != '.');
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(NULL);
cin >> n >> m;
g.resize(n);
for (int i = 0; i < n; i++){
cin >> g[i];
}
vector<vector<int>> depth(n, vector<int> (m));
deque<pair<int, int>> q;
q.push_back({0, 0});
depth[0][0] = 1;
int ans = 1;
while(!q.empty()){
auto [u, v] = q.front();
q.pop_front();
ans = max(ans, depth[u][v]);
for (int i = 0; i < 4; i++){
int cx = X[i] + u;
int cy = Y[i] + v;
if (is_Valid(cx, cy) && depth[cx][cy] == 0){
if (g[cx][cy] == g[u][v]){
depth[cx][cy] = depth[u][v];
q.push_front({cx, cy});
}
else {
depth[cx][cy] = depth[u][v] + 1;
q.push_back({cx, cy});
}
}
}
}
cout << ans << "\n";
}
