#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;
#ifndef ONLINE_JUDGE
// #include "DEBUG.h"
#else
#define debug(...) 69
#endif
#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define int long long
#define double long double
#define endl '\n'
#define Endl cout<<'\n';
#define MOD 1000000007
const int M = 1e18;
const int mod=1e9+7;
double pi = 2 * acos(0.0);
#define I =in()
#define S =sin()
#define C =chin()
#define rep(i,a,b) for(int i=a;i<b;i++)
#define repo(i,a,b) for(int i=a;i>=b;i--)
#define vfill(arr) for(auto &x:arr)cin>>x;
#define Vfill(arr) for(auto &x:arr)for(auto &y:x)cin>>y;
#define Fill(arr) for(int i =0;i<n;i++){cin>>arr[i].first>>arr[i].second;}
#define all(x) begin(x), end(x)
#define unik(vec) vec.resize(unique(all(vec)) - vec.begin());
#define unikSort(vec) sort(all(vec));vec.resize(unique(all(vec)) - vec.begin());
#define vi vector<int>
#define pii pair<int,int>
#define N n
#define vvi vector<vector<int>>
#define pii pair<int,int>
#define pci pair<char,int>
#define psi pair<string,int>
#define mii map<int,int>
#define msi map<string,int>
#define mci map<char,int>
#define vii vector<pair<int,int>>
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define vprint(arr) for(auto &x:arr)cout<<x<<" ";
#define Vprint(arr) for(auto &x:arr){for(auto &y:x)cout<<y<<" ";cout<<endl;}
#define sprint(arr) for(auto &x:arr)cout<<x;cout<<endl;
#define Sprint(arr) for(auto &x:arr){for(auto y:x)cout<<y;cout<<endl;}
inline int in(){int x;cin >> x;return x;}inline string sin(){string x;cin >> x;return x;}inline char chin(){char x;cin >> x;return x;}inline int In(){int x;cin >> x;return x;}
// ==========================================================================================================
long long binpow(long long a, long long b) {if (b == 0)return 1;long long res = binpow(a, b / 2);if (b % 2)return res * res * a;else return res * res;}
// long long binpowMOD(long long a, long long b, long long m) {a %= m;long long res = 1;while (b > 0) {if (b & 1)res = res * a % m;a = a * a % m;b >>= 1;}return res;}
// ==========================================================================================================
// int powm(int a, int b, int mod) { int res = 1; while (b > 0) { if (b & 1)res = (res * a) % mod; a = (a * a) % mod; b = b >> 1; } return res; } //power modulo m
// void extendgcd(int a, int b, int* v) { if (b == 0) { v[0] = 1; v[1] = 0; v[2] = a; return; } extendgcd(b, a % b, v); int x = v[1]; v[1] = v[0] - v[1] * (a / b); v[0] = x; return; } //pass an array of size 3
// int mminv(int a, int b) { int arr[3]; extendgcd(a, b, arr); return arr[0]; } //for non prime b
// int mminvprime(int a, int b) { if (a % b == 0) return -1; return powm(a, b - 2, b); } //for prime only
// const int SIZE = 10005;
// int fact[SIZE], ifact[SIZE];
// void gen_factorial(int n, int mod) { fact[0] = fact[1] = ifact[0] = ifact[1] = 1; for (int i = 2; i <= n; i++) { fact[i] = (i * fact[i - 1]) % mod; } ifact[n] = mminvprime(fact[n], mod); for (int i = n - 1; i >= 2; i--) { ifact[i] = ((i + 1) * ifact[i + 1]) % mod; } }
// int choose(int n, int r, int m) { int val1 = fact[n]; int val2 = ifact[n - r]; int val3 = ifact[r]; return (((val1 * val2) % m) * val3) % m; }
// be careful with mod subtraction - if it is negative than add mod.
// go for another approach
// time complexity
int dx[]={1,-1,0,0};
int dy[]={0,0,1,-1};
vector<string>arr;
int depth[4005][4005];
bool in(int x, int y, int n, int m){
return (x>=0&&x<n&&y>=0&&y<m && arr[x][y]!='.');
}
void solve(int xx){
int n I,m I;
arr.resize(n);vfill(arr);
deque<pii>q;
int ans = 1;
q.push_back({0,0});
depth[0][0]=1;
while(!q.empty()){
int x=q.front().first,y=q.front().second;
q.pop_front();
ans = max(ans,depth[x][y]);
rep(i,0,4){
int newx=x+dx[i];
int newy=y+dy[i];
if(in(newx,newy,n,m)&&depth[newx][newy]==0){
if(arr[x][y]!=arr[newx][newy]){
q.push_back({newx,newy});
depth[newx][newy]=depth[x][y]+1;
}else{
q.push_front({newx,newy});
depth[newx][newy]=depth[x][y];
}
}
}
}
cout<<ans<<endl;
}
// =======================================================================================================
signed main(){
IOS;
int t =1,xx=0 ;
// cin>>t;
while (t--){solve(xx++);}return 0;
}
// =======================================================================================================
