#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define ins insert
#define pb push_back
#define endl '\n'
#define putr(x) cout<<x<<endl;return;
#define all(x) x.begin(),x.end()
const int mod = 1e9 +7, sze = 4e3 +5, inf = INT_MAX, LL = 30;
int depth[sze][sze];
char arr[sze][sze];
const int dx[4] = {-1,1,0,0};
const int dy[4] = {0,0,-1,1};
int n,m;
void rush(){
cin>>n>>m;
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
depth[i][j]=inf;
cin>>arr[i][j];
}
}
deque<pair<int,int>> q;
q.push_back({0,0});
depth[0][0]=1;
int ans=1;
while(!q.empty()){
pair<int,int> node = q.front();
q.pop_front();
ans=max(ans,depth[node.first][node.second]);
for(int i=0;i<4;i++){
int x=node.first + dx[i];
int y=node.second + dy[i];
if(min(x,y)>=0 && x<n && y<m && arr[x][y]!='.'){
if(depth[x][y] >( depth[node.first][node.second] + (arr[node.first][node.second]!=arr[x][y]) )){
depth[x][y] = ( depth[node.first][node.second] + (arr[node.first][node.second]!=arr[x][y]) );
if(arr[x][y]==arr[node.first][node.second]){
q.push_front({x,y});
}
else{
q.push_back({x,y});
}
}
}
}
}
putr(ans);
}
signed main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int tt = 1;
// cin>>tt;
while(tt--){
rush();
}
return 0;
}
