#include <bits/stdc++.h>
#include<iostream>
#include<iomanip>
#include<algorithm>
#include<vector>
#include<utility>
#include<set>
#include<unordered_set>
#include<list>
#include<iterator>
#include<deque>
#include<queue>
#include<stack>
#include<set>
#include<bitset>
#include<random>
#include<map>
#include<unordered_map>
#include<stdio.h>
#include<complex>
#include<math.h>
#include<cstring>
#include<chrono>
#include<string>
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("no-stack-protector")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx,tune=native")
// #pragma GCC optimize("fast-math")
using namespace std;
#define pb push_back
#define ff first
#define ss second
#define vi vector <int>
#define vvi vector <vi>
#define pii pair<int, int>
#define ppi pair<pii, int>
#define vii vector<pii>
#define mii map<int, int>
#define mci map<char, int>
#define miv map<int, vi>
#define mis map<int, set<int>>
#define setbits(n) __builtin_popcount(n)
#define all(v) (v).begin(), (v).end()
#define yes cout<<"YES"<<endl
#define no cout<<"NO"<<endl
#define endl "\n"
#define fo(i,n) for(int i=0;i<n;i++)
#define in(a,n) for(int i=0;i<n;i++) cin>>a[i];
#define show2(a, b) cout<<a<<' '<<b<<endl
#define show3(a, b, c) cout<<a<<' '<<b<<' '<<c<<endl
#define show(arr) for (auto i:arr) cout<<i<<' ';
#define Endl endl
const long long N=1e6+5;
const long long mod=1000000007; //998244353;
int n,m,ans;
string s[4005];
vvi d;
int a[]={-1,0,0,1};
int b[]={0,-1,1,0};
bool inrange(int x, int y)
{
return x>=0 && x<n && y>=0 && y<m && s[x][y]!='.';
}
void bfs()
{
deque<pii> q;
q.pb(pii({0,0}));
d[0][0]=1;
while(q.size())
{
auto p=q.front();q.pop_front();
int x=p.ff,y=p.ss;
ans=max(ans,d[x][y]);
for(int k=0;k<4;k++)
{
int u=x+a[k],v=y+b[k];
if(inrange(u,v))
{
if(s[u][v]!=s[x][y] && d[u][v]>1+d[x][y])
{
d[u][v]=1+d[x][y];q.pb({u,v});
}
else if(s[u][v]==s[x][y] && d[u][v]>d[x][y])
{
d[u][v]=d[x][y];q.push_front({u,v});
}
}
}
}
}
void cases(){
cin>>n>>m;ans=1;
for(int i=0;i<n;i++)cin>>s[i];
d.assign(n,vi(m,N));
bfs();
cout<<ans<<endl;
}
int32_t main(){
std::ios::sync_with_stdio(false);
cin.tie(NULL);cout.tie(NULL);
int t=1;
// cin>>t;
for (int i=0; i<t; i++){
//cout<<"Case #"<<i+1<<": ";
cases();
}
return 0;
}
