#pragma GCC optimize("Ofast")
#pragma GCC optimization ("unroll-loops")
#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp> // Common file
//#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
using namespace std;
//using namespace __gnu_pbds;
#define gc getchar_unlocked
#define fo(i,n) for(ll i=0;i<n;i++)
#define Fo(i,k,n) for(ll i=k;i<n;i++)
#define ll long long
#define si(x) scanf("%d",&x)
#define sl(x) scanf("%I64d",&x)
#define ss(s) scanf("%s",s)
#define pb push_back
#define F first
#define S second
#define clr(x) memset(x, 0, sizeof(x))
#define tr(it, a) for(auto it = a.begin(); it != a.end(); it++)
#define all(x) x.begin(), x.end()
#define PI 3.1415926535897932384626
#define deb(x) cout << #x << " " << x << "\n";
#define INP(v) for(auto &x:v){cin >> x;}
#define OUT(v) for(auto &x:v){cout << x << " ";}
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
const ll mod = 1000000007;
const ll N = 2e5;
const ll Fact_Length = 5e5 + 100;
//template<class T> using oset =tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update> ;
// A.find_by_order(k-1) // gives kth smallest element
// A.order_of_key(x) // no. of elements which are less than x
//Takes a&b as input and Returns : The power (a,b), (a^b)%mod
/*ll Power(ll base, ll expo)
{
ll $result=1; base%=mod;
while(expo) { if(expo%2==1) $result=($result*base)%mod; base=(base*base)%mod; expo/=2; }
return $result;
}
// It give the modulo inverse of a, (1/a)%mod
ll Mod_Inv(ll $a) { return Power($a,mod-2); }
ll Factorial[Fact_Length];
// It make the above Factorial[i] = i! array
ll Make_Factorial()
{
Factorial[0]=1;
for(ll i=1;i<Fact_Length;i++) { Factorial[i]=(i*Factorial[i-1])%mod; } return 0;
}
ll Implement_Make_Factorial=Make_Factorial(); //To Implement Make_Factorial
// Takes n&r as input and Returns : nCr%mod
ll nCr(ll $n,ll $r)
{
if($n<$r || $n<0 || $r<0) return 0;
//if($n>Fact_Length) { cout<<"Error"<<endl; return; }
ll $ans=(Factorial[$n]*Mod_Inv(Factorial[$r]))%mod;
$ans=($ans*Mod_Inv(Factorial[$n-$r]))%mod;
return $ans;
}*/
/*void seive(ll n){
for(ll i=2; i*i<=n; i++){
if(a[i]==0){
for(ll j=i; i*j<=n; j++){
a[i*j] = 1;
}
}
}
}*/
/*ll pw(ll a,ll b){
if(b==0)return 1;
ll t=pw(a,b/2);
if(b%2)return ((a*t*t)%mod);
else return ((t*t)%mod);
}
*/
ll depth[4000][4000];
string snow[4000];
ll dx[] = {0,0,1,-1};
ll dy[] = {1,-1,0,0};
ll n,m;
bool valid(ll x,ll y){
if(x<0 || x>n-1){return false;}
if(y<0 || y>m-1){return false;}
return (snow[x][y] != '.');
}
void solve(){
cin >> n >> m;
fo(i,n){
cin >> snow[i];
}
deque <pll> q;
q.pb({0,0});
ll ans = 1;
depth[0][0] = 1;
while(!q.empty()){
pll p = q.front();
q.pop_front();
ans = max(ans,depth[p.F][p.S]);
fo(i,4){
ll x = p.F+dx[i];
ll y = p.S+dy[i];
if(valid(x,y) && depth[x][y]==0){
if(snow[x][y]==snow[p.F][p.S]){
q.push_front({x,y});
depth[x][y] = depth[p.F][p.S];
}
else{
q.push_back({x,y});
depth[x][y] = depth[p.F][p.S]+1;
}
}
}
}
cout << ans << endl;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll darshit = 1;
//cin >> darshit;
for(ll i=1;i<=darshit;i++)
{
//cout <<"Case #" << i <<": ";
solve();
}
return 0;
}
