#include <bits/stdc++.h>
using namespace std;
/*
#include<Luck>
Compete against Yourself.
Author - swayam_wish
*/
#define ll long long
#define pii pair<ll, ll>
#define piii pair<ll, pair<ll, ll>>
#define pis pair<int, string>
#define db double
int mod = 1e9+7;
ll gcd(ll a, ll b){
if(min(a,b) == 0){
return max(a,b);
}
if((a%b) == 0){
return b;
}
return gcd(b,a%b);
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int t;
t = 1;
while(t--){
int h , w;
cin >> h >> w;
vector<vector<char>> grid(h,vector<char>(w));
for(int i = 0; i<h; i++){
for(int j = 0; j<w; j++){
cin >> grid[i][j];
}
}
vector<vector<int>> vis(h,vector<int>(w,0));
deque<pii> dq;
dq.push_back({0,0});
int delx[] = {0,0,1,-1};
int dely[] = {1,-1,0,0};
vis[0][0] = 1;
int ans = 1;
while(!dq.empty()){
auto it = dq.front();
dq.pop_front();
int x = it.first;
int y = it.second;
int cost = vis[x][y];
ans = max(ans,cost);
for(int i = 0 ; i<4; i++){
int cx = x + delx[i];
int cy = y + dely[i];
if(cx<0 || cy<0 || cx==h || cy==w || vis[cx][cy]!=0 || grid[cx][cy]=='.'){
continue;
}
int wt = (grid[cx][cy] == grid[x][y]) ? 0 : 1;
int tot = cost + wt;
vis[cx][cy] = tot;
if(wt){
dq.push_back({cx,cy});
}
else{
dq.push_front({cx,cy});
}
}
}
cout<<ans<<endl;
}
}
