#include<bits/stdc++.h>
using namespace std;
int main() {
int n, m;
cin>>n>>m;
vector<string> v(n);
for (int i = 0; i<n; i++) cin>>v[i];
vector<pair<int, int>> moves;
moves.push_back({1,0});
moves.push_back({0,1});
moves.push_back({-1,0});
moves.push_back({0,-1});
vector<vector<int>> depth(n, vector<int> (m));
deque<pair<int, int>> q;
depth[0][0] = 1;
int ans = 1;
q.push_front({0, 0});
while(!q.empty()) {
int x = q.front().first;
int y = q.front().second;
q.pop_front();
ans = max(depth[x][y], ans);
for (auto move: moves) {
int new_x = x + move.first;
int new_y = y + move.second;
if (new_x<n && new_x>=0 && new_y<m && new_y>=0 && depth[new_x][new_y] == 0 && v[new_x][new_y] != '.') {
if (v[new_x][new_y] == v[x][y]) {
depth[new_x][new_y] = depth[x][y];
q.push_front({new_x, new_y});
}
else {
depth[new_x][new_y] = 1 + depth[x][y];
q.push_back({new_x, new_y});
}
}
}
}
cout<<ans;
}
