#include "bits/stdc++.h"
using namespace std;
#define pb push_back
#define ff first
#define ss second
#define endl "\n"
#define MOD 1000000007
#define int long long
#define double long double
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define what_is(x) cerr << #x << " is " << x << endl;
const int N=200005;
const long long INF = LLONG_MAX;
const int INF2=(int)1e18;
const int LOG=20;
typedef pair<int,int> pii;
typedef tuple<int,int,int> tp;
typedef priority_queue<pii,vector<pii>,greater<pii>> min_pq;
typedef priority_queue<pii> max_pq;
typedef long long ll;
//sunlari dusun//
/*
* kodu kisaltcak fonksiyon
* cevaba binary search ya da normal bs
* segment tree / sparse table
* stack
* teklik ciftlik
* precomputation
* EN ONEMLISI OVERKILLEME
* edge case dusunr
* constraintlere bak
* indisleri kontrol et
* dp
* greedy
* sorting
* dfs bfs
* sieve
*/
bool vis[1001][1001];
char arr[1001][1001];
int n,m,cnt=0;
queue<tuple<int,int,char>> q;
queue<tuple<int,int,char>> q2;
void dfs(int a,int b,char x)
{
//cout << "a:" << a << " b: " << b << " x: " << x << endl;
if(vis[a][b])
{
return;
}
vis[a][b]=1;
if(a+1<=n && !vis[a+1][b] && arr[a+1][b]!='*')
{
if(arr[a+1][b]==x)
{
dfs(a+1,b,x);
}
else
{
q2.push({a+1,b,(x=='B' ? 'T' : 'B')});
}
}
if(a-1>=1 && !vis[a-1][b] && arr[a-1][b]!='*')
{
if(arr[a-1][b]==x)
{
dfs(a-1,b,x);
}
else
{
q2.push({a-1,b,(x=='B' ? 'T' : 'B')});
}
}
if(b+1<=m && !vis[a][b+1] && arr[a][b+1]!='*')
{
if(arr[a][b+1]==x)
{
dfs(a,b+1,x);
}
else
{
q2.push({a,b+1,(x=='B' ? 'T' : 'B')});
}
}
if(b-1>=1 && !vis[a][b-1] && arr[a][b-1]!='*')
{
if(arr[a][b-1]==x)
{
dfs(a,b-1,x);
}
else
{
q2.push({a,b-1,(x=='B' ? 'T' : 'B')});
}
}
}
void solve()
{
cin >> n >> m;
for(int i=1;i<=n;i++) for(int j=1;j<=m;j++) cin >> arr[i][j];
q2.push({1,1,(arr[1][1]=='B' ? 'B' : 'T')});
while(!q2.empty())
{
cnt++;
while(!q2.empty())
{
q.push(q2.front());
//cout << get<0>(q2.front()) << " " << get<1>(q2.front()) << endl;
q2.pop();
}
while(!q.empty())
{
tuple<int,int,char> cur=q.front();
q.pop();
// cout << "a" << "\n";
dfs(get<0>(cur),get<1>(cur),get<2>(cur));
}
}
cout << cnt << endl;
}
int32_t main(){
cin.tie(0); ios::sync_with_stdio(0);
cout << fixed << setprecision(15);
int t=1;//cin>> t;
while(t--) solve();
return 0;
}
