#include <bits/stdc++.h>
using namespace std;
int dx[4]{1,-1,0,0}, dy[4]{0,0,1,-1};
int n,m, ans = 1;
vector<vector<int>> depth;
vector<string> snow;
bool inside(int x,int y){
return (x > -1 && x < n && y > -1 && y < m && snow[x][y] != '.');
}
int main(){
cin >> n >> m;
depth.resize(n,vector<int>(m,0));
snow.resize(n);
for(int i = 0;i < n;i++){
cin >> snow[i];
//cout << snow[i].length();
//cout << "\n";
}
deque<pair<int,int>> q;
q.push_back({0,0});
depth[0][0] = 1;
while(!q.empty()){
pair<int,int> c = q.front();
q.pop_front();
ans = max(ans, depth[c.first][c.second]);
for(int i = 0;i < 4;i++){
int x = c.first + dx[i],y = c.second + dy[i];
if(inside(x,y) && !depth[x][y]){
if(snow[x][y] == snow[c.first][c.second]){
depth[x][y] = depth[c.first][c.second];
q.push_front({x,y});
}
else{
depth[x][y] = depth[c.first][c.second] + 1;
q.push_back({x,y});
}
}
}
}
cout << ans;
return 0;
}
