#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(), x.end()
#define srtl(x)sort(all(x))
#define srtg(x)sort((x).begin(),(x).end(),greater<>())
#define rev(x) reverse(all(x))
#define lb(x,y) lower_bound(x.begin(),x.end(),y)-x.begin()
#define ub(x,y) upper_bound(x.begin(),x.end(),y)-x.begin()
#define ios ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define f first
#define s second
#define pb push_back
#define ins insert
#define nxt(x) next_permutation(all(x))
#define _b __builtin_popcount
#define ve vector
#define pii pair<int,int>
#define piii pair<int,pii>
#define vi vector<int>
#define vii vector<pii>
#define viii vector<piii>
#define vvi vector<vi>
//#define vs vector<string>
#define vb vector<bool>
#define pV(x)for(auto i:x)cout<<i<<" ";
#define geta(a){for(auto &i:a)cin>>i;}
#define fr(n)for(int i=0;i<n;i++)
#define Fr(n)for(int i=n-1;i>=0;i--)
#define suma(a)accumulate(a.begin(),a.end(),0LL)
#define br(x){cout<<x<<"\n";return;}
#define yesn cout<<"YES\n";
#define yes()br("YES");
#define no(){br("NO")}
#define alice() br("Alice");
#define bob() br("Bob");
#define cn continue;
#define cint const int
#define int long long
int mod=1000000007;
cint mod1=100000007;
cint mod2=998244353;
int ax[8]={0,1,0,-1,-1,1,1,-1};
int ay[8]={1,0,-1,0,1,-1,1,-1};
//int euc(int a,int b,int c,int d){return abs(a-c)+abs(b-d);}
int bp(int x,int y){
if(y==0)return 1;
int r=bp(x,y/2);
return (y&1)?r*r%mod*x%mod:r*r%mod;
}
int bpm(int x,int y){
if(y==0)return 1;
int r=bp(x,y/2);
return (y&1)?r*r*x:r*r;
}
int cinn(){
int n;
cin>>n;
return n;
}
#define w cinn()
vvi dis(5000,vi(5000,1e18));
int n,m;
ve<string>mat(5000);
bool to(int x,int y){
if(x<0||y<0||x>=n||y>=m||mat[x][y]=='.')return 0;
return 1;
}
void solve(){
cin>>n>>m;
fr(n){cin>>mat[i];}
deque<pii>q;
int ans=0;
dis[0][0]=1;
q.push_back({0,0});
while(!q.empty()){
pii p=q.front();q.pop_front();
fr(4){
int x=p.f+ax[i],y=p.s+ay[i];
if(!to(x,y))cn;
if(mat[x][y]!=mat[p.f][p.s]&&dis[x][y]>dis[p.f][p.s]+1){
dis[x][y]=min(dis[x][y],dis[p.f][p.s]+1);
q.push_back({x,y});
}
else if(mat[x][y]==mat[p.f][p.s]&&dis[x][y]>dis[p.f][p.s]){
dis[x][y]=min(dis[x][y],dis[p.f][p.s]);
q.push_front({x,y});
}
}
}
fr(n){
for(int j:dis[i])if(j!=1e18)ans=max(ans,j);
}
cout<<ans;
}
int32_t main(){
ios;
int t=1;
//cin>>t;
while(t--){
solve();
}
return 0;
}
/*
5 8
FFR.....
.FRRR...
.FFFFF..
..RRRFFR
.....FFF
*/
