//#pragma GCC optimize("O3,unroll-loops,Ofast")
//#pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
using namespace std;
// using namespace __gnu_pbds;
#define MAX 10005
#define pb push_back
// #define mp make_pair
#define int long long
#define f first
#define s second
#define vi vector<int>
#define pii pair<int,int>
#define si set<int>
#define vpii vector<pair<int,int>>
const int mod = 1e9+7;
const double INF = 1e18;
// myMap.begin()->first : key
// myMap.begin()->second : value
int epow(int a,int b){int ans=1;while(b){if(b&1) ans*=a;a*=a;b>>=1;ans%=mod;a%=mod;}return ans%mod;}
int gcd(int a,int b) {if(a<b)swap(a,b);while(b){int tmp=b;b=a%b;a=tmp;}return a;}
int mul(int a,int b){return ((a%mod)*(b%mod))%mod;}
int sum(int a,int b){return ((a%mod)+(b%mod))%mod;}
//typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
// typedef
// tree<int,null_type,less_equal<int>,rb_tree_tag,tree_order_statistics_node_update>ordered_multiset;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
int n,m;
vector<vi> d(505,vi(505));
vector<vector<char>> grid(505,vector<char>(505));
bool valid(int a,int b){
if(a>0 && b>0 && a<=n && b<=m && grid[a][b]!='.') return true;
return false;
}
void solve(){
cin>>n>>m;
for(int i=1;i<=n;i++) for(int j=1;j<=m;j++) cin>>grid[i][j];
deque<pii> q; q.push_back({1,1}); d[1][1]=1;
while(q.size()){
pii node=q.front(); q.pop_front();
for(int i=0;i<4;i++){
int x=node.f+dx[i], y=node.s+dy[i];
if(!valid(x,y) || d[x][y]!=0 ) continue;
d[x][y]=d[node.f][node.s]+(grid[node.f][node.s]!=grid[x][y]);
if(grid[node.f][node.s]!=grid[x][y]) q.push_back({x,y});
else q.push_front({x,y});
}
}
int ans=1;
for(int i=1;i<=n;i++) for(int j=1;j<=n;j++) ans=max(ans,d[i][j]);
cout<<ans<<endl;
}
int32_t main(/*int32_t argc, char* argv[]*/){
std::ios_base::sync_with_stdio(0); std::cin.tie(0);
// freopen("odometer.in", "r", stdin);
// freopen("odometer.out", "w", stdout);
int t=1;
// cin >> t;
while (t--) solve();
return 0;
}
