#include<bits/stdc++.h>
using namespace std;
int H, W;
vector<string> snow;
vector<vector<int>> distances;
int bfs(){
deque<int> DQ;
distances[0][0] = 1;
int ans = 1;
DQ.push_back(0);
while(!DQ.empty()){
int actual = DQ.front(); DQ.pop_front();
int x = actual/W;
int y = actual - W*x;
ans = max(ans, distances[x][y]);
if(x){
if(distances[x-1][y] == -1){
if(snow[x-1][y] == snow[x][y]){
distances[x-1][y] = distances[x][y];
DQ.push_front((x-1)*W + y);
}
else if (snow[x-1][y] != '.'){
distances[x-1][y] = distances[x][y]+1;
DQ.push_back((x-1)*W + y);
}
}
}
if(y){
if(distances[x][y-1] == -1){
if(snow[x][y-1] == snow[x][y]){
distances[x][y-1] = distances[x][y];
DQ.push_front((x)*W + y-1);
}
else if (snow[x][y-1] != '.'){
distances[x][y-1] = distances[x][y]+1;
DQ.push_back((x)*W + y-1);
}
}
}
if(x < (H-1)){
if(distances[x+1][y] == -1){
if(snow[x+1][y] == snow[x][y]){
distances[x+1][y] = distances[x][y];
DQ.push_front((x+1)*W + y);
}
else if (snow[x+1][y] != '.'){
distances[x+1][y] = distances[x][y]+1;
DQ.push_back((x+1)*W + y);
}
}
}
if(y < (W-1)){
if(distances[x][y+1] == -1){
if(snow[x][y+1] == snow[x][y]){
distances[x][y+1] = distances[x][y];
DQ.push_front((x)*W + y + 1);
}
else if (snow[x][y+1] != '.'){
distances[x][y+1] = distances[x][y]+1;
DQ.push_back((x)*W + y + 1);
}
}
}
}
return ans;
}
int main(){
cin >> H >> W;
snow = vector<string>(H);
for(int i = 0; i < H; ++i)cin >> snow[i];
distances = vector<vector<int>>(H, vector<int>(W, -1));
cout << bfs()<< endl;
return 0;
}
