// Jai Shree Ram
#include<bits/stdc++.h>
using namespace std;
/* Abhi-Atg */
#define array int n;cin >> n;vector<long long> v(n);f(i,0,n)cin >> v[i];
#define out(_) for (auto &it :_){cout << it << " " ;}cout<<endl;
#define f(i,l,r) for(int i=l;i<r;i++)
#define ff(i,r,l) for(int i=r;i>=l;i--)
#define pb push_back
#define mod 1000000007
#define INDIA 998244353
#define ll long long
#define all(v) v.begin(),v.end()
#define dbg cout << "Bharat\n"
#define yes cout << "YES\n"
#define no cout << "NO\n"
#define minus cout << "-1\n"
void solve(){
int n,m;cin >> n >> m;
vector<string> v(n);
for(int i=0;i<n;i++){
cin >> v[i];
}
vector<vector<int>> vis(n,vector<int>(m,0));
vector<pair<int,int>> q;
vector<int> x={0,0,1,-1};
vector<int> y={1,-1,0,0};
q.push_back({0,0});
vis[0][0]=1;
int ans=0;
while(q.size()){
vector<pair<int,int>> p;
for(int i=0;i<q.size();i++){
for(int j=0;j<4;j++){
int a=q[i].first+x[j];
int b=q[i].second+y[j];
if(a>=0 && a<n && b>=0 && b<m && v[a][b]!='.' && vis[a][b]==0){
if(v[a][b]==v[q[i].first][q[i].second]){
q.push_back({a,b});
vis[a][b]=1;
}
else{
p.push_back({a,b});
vis[a][b]=1;
}
}
}
}
q=p;
ans++;
}
cout<<ans<<"\n";
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(nullptr);
// #ifndef ONLINE_JUDGE
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
// #endif
// freopen("input.in", "r", stdin);
// freopen("output.out", "w", stdout);
int t=1;
// cin >> t;
for(int _=1;_<=t;_++){
// cout<<"Case #"<<_<<": ";
solve();
}
return 0;
}
