#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <fstream>
#define endl '\n'
#define int long long
#define mod 1000000007
using namespace std;
char m[4001][4001];
int dx[] = {0,0,1,-1};
int dy[] = {1,-1,0,0};
int dist[4001][4001];
signed main(){
int h,w, ans = 0; cin >> h >> w;
for(int i = 0; i < h; i++){
for(int j = 0; j < w; j++){
cin >> m[i][j];
}
}
dist[0][0] = 1;
deque<pair<int,int>>d;
d.push_front({0,0});
while(d.size()){
auto x = d.front();
ans = max(ans, dist[x.first][x.second]);
d.pop_front();
for(int i = 0; i < 4; i++){
int aa = x.first + dx[i], bb = x.second + dy[i];
int val = dist[x.first][x.second];
if(aa < 0 or bb < 0 or aa >= h or bb >= w) continue;
if(m[aa][bb] == '.' or dist[aa][bb] != 0) continue;
if(m[aa][bb] != m[x.first][x.second]){
dist[aa][bb] = val + 1;
d.push_back({aa,bb});
}else{
dist[aa][bb] = val;
d.push_front({aa,bb});
}
}
}
cout << ans;
}
