#include<bits/stdc++.h>
using namespace std;
int H, W;
vector<string> snow;
int dijkstra(){
vector<int> distances(H*W, -1);
int maxDist = 0;
priority_queue<vector<int>> PQ;
PQ.push({0, 0, 0});
while(!PQ.empty()){
vector<int> act = PQ.top(); PQ.pop();
int x = act[1];
int y = act[2];
int d = -act[0];
int position = x*W + y;
if(distances[position] != -1) continue;
distances[position] = d;
maxDist = max(maxDist, d);
if(x){
int nextPos = (x-1)*W + y;
if(distances[nextPos] == -1){
if(snow[x-1][y] == snow[x][y])PQ.push({-d, x-1, y});
else if (snow[x-1][y] != '.') PQ.push({-d-1, x-1, y});
}
}
if(y){
int nextPos = x*W + y - 1;
if(distances[nextPos] == -1){
if(snow[x][y-1] == snow[x][y]) PQ.push({-d, x, y-1});
else if(snow[x][y-1] != '.') PQ.push({-d-1, x, y-1});
}
}
if(x < (H-1)){
int nextPos = (x+1)*W + y;
if(distances[nextPos] == -1){
if(snow[x+1][y] == snow[x][y])PQ.push({-d, x+1, y});
else if(snow[x+1][y] != '.') PQ.push({-d-1, x+1, y});
}
}
if(y < (W-1)){
int nextPos = x*W + y + 1;
if(distances[nextPos] == -1){
if(snow[x][y+1] == snow[x][y]) PQ.push({-d, x, y+1});
else if (snow[x][y+1] != '.') PQ.push({-d-1, x, y+1});
}
}
}
return maxDist;
}
int main(){
cin >> H >> W;
snow = vector<string>(H);
for(int i = 0; i < H; ++i)cin >> snow[i];
cout << dijkstra()+1 << endl;
return 0;
}
