#pragma GCC optimize("Ofast" , "unroll-loops")
#include<bits/stdc++.h>
#define bit(i , j) ((j >> i) & 1)
#define fi first
#define se second
#define all(x) (x).begin() , (x).end()
using namespace std;
#define int long long
#define pll pair<int , int>
const int MAXN = 4040;
char a[MAXN][MAXN];
int d[MAXN][MAXN];
int dx[4] = {-1 , 0 , 1 , 0};
int dy[4] = {0 , -1 , 0 , 1};
const int inf = 1e9+1;
int32_t main(){
//freopen("A.inp", "r", stdin);
//freopen("robot.out", "w", stdout);
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n , m; cin >> n >> m;
for(int i = 1 ; i <= n ; i++){
for(int j = 1 ; j <= m ; j++) cin >> a[i][j];
}
deque<pll> Q;
for(int i = 1 ; i <= n ; i++){
for(int j = 1; j <= m ; j++) d[i][j] = -1;
}
auto out = [&](int x , int y){
return (x < 1 || x > n || y < 1 || y > m);
};
Q.push_back({1 , 1});
d[1][1] = 0;
while(Q.size()){
pll t = Q.front();
Q.pop_front();
for(int i = 0 ; i < 4 ; i++){
int x = t.fi + dx[i] , y = t.se + dy[i];
if(out(x , y)) continue;
if(d[x][y] == -1 && a[x][y] != '.'){
if(a[x][y] == a[t.fi][t.se]) d[x][y] = d[t.fi][t.se] , Q.push_front({x , y});
else d[x][y] = d[t.fi][t.se] + 1, Q.push_back({x , y});
}
}
}
int ans = 0;
for(int i = 1 ; i <= n ; i++) for(int j = 1 ; j <= m ; j++) ans = max(ans , d[i][j]);
cout << ans << "\n";
return 0;
}
