#include <bits/stdc++.h>
using namespace std;
const int MN = 4000;
string grid[MN] = {};
int dist[MN][MN] = {{}};
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
int main(){
cin.tie(0)->sync_with_stdio(0);
int H, W; cin >> H >> W;
for(int i = 0; i < H; i++){
cin >> grid[i];
}
int maxDist = 1;
dist[0][0] = 1;
deque<pair<int,int>> d; d.push_front({0,0});
while(!d.empty()){
pair<int,int> p = d.front(); d.pop_front();
int x = p.first; int y = p.second;
for(int i = 0; i < 4; i++){
int x_ = x+dx[i]; int y_ = y+dy[i];
if(x_ < 0 || x_ >= H || y_ < 0 || y_ >= W) continue;
if(grid[x_][y_] == '.' || dist[x_][y_] > 0) continue;
if(grid[x_][y_] == grid[x][y]){
dist[x_][y_] = dist[x][y];
d.push_front({x_,y_});
} else{
dist[x_][y_] = dist[x][y]+1;
maxDist = max(maxDist, dist[x_][y_]);
d.push_back({x_,y_});
}
}
}
cout << maxDist;
}
