#ifndef _Alignof
#define _Alignof(x) __alignof__(x)
#endif
#include<bits/stdc++.h>
#include<ext/pb_ds/tree_policy.hpp>
#include<ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#define vll vector<long long>
#define vpll vector< pair<long long int , long long int > >
#define rep(i,x,a) for (long long i=x; i<a; i++)
#define si(x) (long long int)x.size()
#define pb push_back
#define ff first
#define ss second
#define lg2(x) (long long int)log2(x)
#define gap " "
#define nl '\n'
#define all(x) (x).begin(),(x).end()
#define no cout<<"No\n"
#define yes cout<<"Yes\n"
#define vld vector<long double>
typedef long long ll;
typedef unsigned long long ull;
typedef long double lld;
#ifndef ONLINE_JUDGE
#define debug(x) cerr << #x <<" "; _print(x); cerr << endl;
#else
#define debug(x)
#endif
void _print(ll t) {cerr << t;}
void _print(int t) {cerr << t;}
void _print(string t) {cerr << t;}
void _print(char t) {cerr << t;}
void _print(lld t) {cerr << t;}
void _print(double t) {cerr << t;}
void _print(ull t) {cerr << t;}
void print(){
cout << '\n';
}
template<class T, class... Ts>
void print(const T& a, const Ts&... b){
cout << a;
(cout << ... << (cout << ' ', b));
cout << '\n';
}
template<class... T>
void input(T&... a){
(cin >> ... >> a);
}
template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);
template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);
template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p) {cerr << "{"; _print(p.ff); cerr << ","; _print(p.ss); cerr << "}";}
template <class T> void _print(vector <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(set <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(multiset <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void _print(map <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int MOD=1e9+7;
const int N=1e6+10;;
const ll INF=1e16;
const long long int LINF=LLONG_MAX;
/*------------------------------------*/
void solve(int tc = 0)
{
ll h,w;input(h,w);
vector<vector<char>> grid(h+1,vector<char>(w+1));
rep(i,0,h){
rep(j,0,w){
cin >> grid[i][j];
}
}
vector<vector<ll>> dis(h+1,vll(w+1,INF));
deque<pair<ll,ll>> q;
vll dx = {0,0,1,-1};
vll dy = {1,-1,0,0};
q.push_back({0,0});
dis[0][0] = 0;
while(!q.empty()){
auto [x,y] = q.front();
q.pop_front();
for(int i=0;i<4;i++){
ll newx = x+dx[i];
ll newy = y+dy[i];
if(newx>=0 && newx<h && newy >=0 && newy < w && grid[newx][newy]!='.' && dis[newx][newy] > (dis[x][y]+(grid[x][y]!=grid[newx][newy]))){
ll w = (grid[x][y]!=grid[newx][newy]);
dis[newx][newy] = dis[x][y]+w;
if(w == 0){
q.push_front({newx,newy});
}
else{
q.push_back({newx,newy});
}
}
}
}
ll ans = 0;
rep(i,0,h){
rep(j,0,w){
if(dis[i][j]!=INF){
ans = max(ans,dis[i][j]);
}
}
}
cout << ans + 1 << nl;
}
/*------------------------------------*/
int main()
{
#ifndef ONLINE_JUDGE
freopen("Error.txt","w",stderr);
#endif
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
ll tc=1;
for(int i=0 ; i < tc ; i++)
{
solve(i);
}
return 0;
}
