#include <bits/stdc++.h>
const long double EPS = 1e-7;
const long long int INF = LONG_LONG_MAX/2;
const long long int M = (long long int) 1e9 + 7;//998'244'353;
using namespace std;
//insert policy here
//insert mintcode here
#if defined (ONLINE_JUDGE) || !__has_include (</home/sidlad/Desktop/Coding Folder/c and cpp codes/Debug.h>)
void _exe() {}
template <typename T, typename... V>
const T& _exe(const T &t,const V&... v) {return t;}
template <typename T, typename... V>
T& _exe(T &t,V&... v) {return t;}
#define debug(x...) (_exe(x))
class CNothing {};
template <typename T>
const CNothing& operator<<(const CNothing& proxy, const T&)
{
return proxy;
}
const CNothing& operator<<(const CNothing& proxy, std::ostream& (*)(std::ostream&))
{
return proxy;
}
CNothing cnothing;
#define cerr cnothing
#else
#include </home/sidlad/Desktop/Coding Folder/c and cpp codes/Debug.h>
#endif
#define int long long
#define double long double
#define all(x) (x).begin(),(x).end()
#define endl "\n" //comment out for interactive problems
#define cout(x) x?cout<<"Yes"<<endl:cout<<"No"<<endl
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
cout.precision(numeric_limits<double>::max_digits10);
// freopen("input.txt","r",stdin);
// freopen("output.txt","w",stdout);
vector<pair<int,int>> dxy = {{-1,0},{1,0},{0,1},{0,-1}};
int n,m;
cin>>n>>m;
vector<vector<char>> v(n,vector<char>(m));
for(auto& row:v)for(auto& ele:row)cin>>ele;
deque<pair<pair<int,int>,int>> dq;
int ans = 1;
dq.push_back({{0,0},1});
while(dq.size())
{
auto [c,d] = dq.front();
dq.pop_front();
auto [i,j] = c;
ans = max(ans,d);
// debug(c,d);
for(auto [dx,dy]:dxy)
{
int idx = i + dx;
int jdy = j + dy;
if(i + dx == -1 or i + dx == n)continue;
if(j + dy == -1 or j + dy == m)continue;
// debug(idx,jdy);
if(v[idx][jdy] == '.')continue;
if(v[idx][jdy] == v[i][j])dq.push_front({{idx,jdy},d});
else dq.push_back({{idx,jdy},d + 1});
}
v[i][j] = '.';
}
cout<<ans<<endl;
}
