// deepanshusau
#pragma GCC optimize ("O3")
#ifdef ONPC
#define _GLIBCXX_DEBUG
#include "debug.cpp"
#else
#define debug(...)
#define debugArr(arr,n)
#endif
#include<bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define ll long long
#define ld long double
#define pii pair<int, int>
#define vi vector<int>
#define F first
#define S second
#define pb push_back
#define PI acos(-1)
#define uid(a, b) uniform_int_distribution<int>(a, b)(rng)
#define int long long
constexpr char sp=' ';
constexpr char nl='\n';
constexpr int MOD=1e9+7;
void solve(){
int n,m;cin>>n>>m;
vector<string> g(n);
for(int i=0;i<n;i++) cin>>g[i];
int ans=0;
vi row={0,0,1,-1},col={1,-1,0,0};
vector<vi> dis(n,vi(m,1)),vis(n,vi(m,0));
deque<pii> dq;
dq.push_back({0,0});
while(sz(dq)){
auto [i,j]=dq.front();
dq.pop_front();
vis[i][j]=1;
ans=max(ans,dis[i][j]);
for(int k=0;k<4;k++){
int x=i+row[k],y=j+col[k];
if(x>=0 && x<n && y>=0 && y<m && vis[x][y]==0 && g[x][y]!='.'){
if(g[x][y]==g[i][j]){
dis[x][y]=dis[i][j];
dq.push_front({x,y});
}
else{
dis[x][y]=dis[i][j]+1;
dq.push_back({x,y});
}
}
}
}
cout<<ans<<nl;
}
signed main(){
clock_t tStart = clock();
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout << setprecision(12) << fixed;
#ifdef ONPC
freopen("debug.txt", "w", stderr);
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
int t=1;
// cin >> t;
while(t--){
solve();
}
#ifdef ONPC
cerr<<'\n'<<"Time taken : "<<((double)(clock()-tStart)/CLOCKS_PER_SEC)*1000<<" ms"<<'\n';
#endif
return 0;
}
