#include <bits/stdc++.h>
using namespace std;
const int N = 4000;
string grid[N];
bool vu[N][N];
int h,w;
vector<pair<int,int>> dir = {{1,0},{0,1},{-1,0},{0,-1}};
struct node{
int x,y,val;
};
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cin >> h >> w;
for (int i=0; i<h; ++i){
cin >> grid[i];
}
deque<node> q;
q.emplace_back(node{0,0,1});
int ans = 0;
while (!q.empty()){
auto f = q.front();
q.pop_front();
ans = max(ans,f.val);
for (auto i:dir){
int nx = i.first+f.x, ny = i.second+f.y;
if (nx >= 0 and ny >= 0 and nx < h and ny < w and !vu[nx][ny] and grid[nx][ny] != '.'){
vu[nx][ny] = true;
if (grid[f.x][f.y] != grid[nx][ny]) q.emplace_back(node{nx,ny,f.val+1});
else q.emplace_front(node{nx,ny,f.val});
}
}
}
cout << ans;
return 0;
}
