/*
Author :: Bot Anshu
~All our knowledge has its origins in our perceptions - Leonardo Da Vinci.
*/
#pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace chrono;
using namespace __gnu_pbds;
#define fastio() ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define MOD 1000000007
#define MOD1 998244353
#define INF 1e18
#define nline "\n"
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define ff first
#define ss second
#define PI 3.141592653589793238462
#define set_bits __builtin_popcountll
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define print(a) for(auto i:a){ cout<<i<<' ' ;}cout<<endl;
#define read(x) int x ; cin>>x;
#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define mt make_tuple
#define eb emplace_back
typedef vector<int> vin;
typedef vector<string> vst;
typedef vector<char> vch;
#ifdef ONLINE_JUDGE
#define debug(x) cerr << #x<<" "; _print(x); cerr << endl;
#else
#define debug(x);
#endif
typedef long long ll;
typedef unsigned long long ull;
typedef long double lld;
// typedef __int128 ell;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update > pbds; // find_by_order, order_of_key
void _print(ll t) {cerr << t;}
void _print(int t) {cerr << t;}
void _print(string t) {cerr << t;}
void _print(char t) {cerr << t;}
void _print(lld t) {cerr << t;}
void _print(double t) {cerr << t;}
void _print(ull t) {cerr << t;}
template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);
template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);
template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p) {cerr << "{"; _print(p.ff); cerr << ","; _print(p.ss); cerr << "}";}
template <class T> void _print(vector <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(set <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(multiset <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void _print(map <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}
void _print(pbds v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
/*---------------------------------------------------------------------------------------------------------------------------*/
ll gcd(ll a, ll b) {if (b > a) {return gcd(b, a);} if (b == 0) {return a;} return gcd(b, a % b);}
ll expo(ll a, ll b, ll mod) {ll res = 1; while (b > 0) {if (b & 1)res = (res * a) % mod; a = (a * a) % mod; b = b >> 1;} return res;}
void extendgcd(ll a, ll b, ll*v) {if (b == 0) {v[0] = 1; v[1] = 0; v[2] = a; return ;} extendgcd(b, a % b, v); ll x = v[1]; v[1] = v[0] - v[1] * (a / b); v[0] = x; return;} //pass an arry of size1 3
ll mminv(ll a, ll b) {ll arr[3]; extendgcd(a, b, arr); return arr[0];} //for non prime b
ll mminvprime(ll a, ll b) {return expo(a, b - 2, b);}
bool revsort(ll a, ll b) {return a > b;}
ll combination(ll n, ll r, ll m, ll *fact, ll *ifact) {ll val1 = fact[n]; ll val2 = ifact[n - r]; ll val3 = ifact[r]; return (((val1 * val2) % m) * val3) % m;}
void google(int t) {cout << "Case #" << t << ": ";}
vector<ll> sieve(int n) {int*arr = new int[n + 1](); vector<ll> vect; for (int i = 2; i <= n; i++)if (arr[i] == 0) {vect.push_back(i); for (int j = 2 * i; j <= n; j += i)arr[j] = 1;} return vect;}
ll mod_add(ll a, ll b, ll m) {a = a % m; b = b % m; return (((a + b) % m) + m) % m;}
ll mod_mul(ll a, ll b, ll m) {a = a % m; b = b % m; return (((a * b) % m) + m) % m;}
ll mod_sub(ll a, ll b, ll m) {a = a % m; b = b % m; return (((a - b) % m) + m) % m;}
ll mod_div(ll a, ll b, ll m) {a = a % m; b = b % m; return (mod_mul(a, mminvprime(b, m), m) + m) % m;} //only for prime m
ll phin(ll n) {ll number = n; if (n % 2 == 0) {number /= 2; while (n % 2 == 0) n /= 2;} for (ll i = 3; i <= sqrt(n); i += 2) {if (n % i == 0) {while (n % i == 0)n /= i; number = (number / i * (i - 1));}} if (n > 1)number = (number / n * (n - 1)) ; return number;} //O(sqrt(N))
ll getRandomNumber(ll l, ll r) {return uniform_int_distribution<ll>(l, r)(rng);}
void usaco(string s){
freopen((s + ".in").c_str(), "r", stdin);
freopen((s +".out").c_str(), "w", stdout);
}
/*--------------------------------------------------------------------------------------------------------------------------*/
int dr[4] = {1, -1, 0, 0};
int dc[4] = {0, 0, 1, -1};
int n,m;
bool isValid (int x, int y) {
if (x < 0 || y < 0 || x>=n || y>=m) return false;
return true;
}
void solve() {
cin>>n>>m;
vector <string> meadow(n);
int foxes = 0, rabbits = 0;
for (auto &it: meadow) {
cin>>it;
}
vector<vector<int>> dis(n, vector<int>(m, INT_MAX));
int animals = 0;
deque <pair<int,int>> dq;
dq.push_back({0, 0});
dis[0][0] = 0;
while (dq.size()) {
pair<int,int> node = dq.front(); dq.pop_front();
int x = node.first, y = node.second;
for (int i = 0; i < 4; i++) {
int nx = x + dr[i], ny = y + dc[i];
if (!isValid(nx, ny) || meadow[nx][ny]=='.') continue;
if (dis[nx][ny] <= 1 + dis[x][y]) continue;
if (meadow[nx][ny] == meadow[x][y]) {
dis[nx][ny] = dis[x][y];
dq.push_front({nx, ny});
} else {
dis[nx][ny] = dis[x][y] + 1;
animals = max(animals, dis[nx][ny]);
dq.push_back({nx, ny});
}
}
}
cout << animals + 1<< '\n';
}
int main() {
fastio();
auto start1 = high_resolution_clock::now();
int t =1;
// cin>>t;
while(t--){
solve();
}
#ifdef ONLINE_JUDGE
auto stop1 = high_resolution_clock::now();
auto duration = duration_cast<microseconds>(stop1 - start1);
cerr <<endl<< "Time: " << duration . count() / 1000 << endl;
#endif
}
