#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long long
#define INF 1000000000
vector<vector<vector<int>>> v;
int bfs(int n, int st){
try{
vector<int> di(n, INF);
deque<int> q;
di[st] = 0;
q.push_back(st);
while (!q.empty()){
int x = q.front();
q.pop_front();
for (auto el : v[x]){
if (di[el[0]] > di[x] + el[1]){
di[el[0]] = di[x] + el[1];
if (el[1] == 0){
q.push_front(el[0]);
}
else{
q.push_back(el[0]);
}
}
}
}
int ans = 0;
for (int i = 0; i < n; i++){
if (di[i] == INF) continue;
ans = max(ans, di[i]);
}
return ans;
}
catch(int exc){
return -1;
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, m;
cin>>n>>m;
v.resize((n + 1) * (m + 1));
vector<string> s(n);
for (int i = 0; i < n; i++){
cin>>s[i];
for (int j = 0; j < m; j++){
if (s[i][j] == '.') continue;
int v1 = i * m + j;
if (i != 0 && s[i - 1][j] != '.'){
int v2 = (i - 1) * m + j;
int va;
if (s[i][j] == s[i - 1][j]){
va = 0;
}
else{
va = 1;
}
v[v1].push_back({v2, va});
v[v2].push_back({v1, va});
}
if (j != 0 && s[i][j - 1] != '.'){
int v2 = i * m + j - 1;
int va;
if (s[i][j] == s[i][j - 1]){
va = 0;
}
else{
va = 1;
}
v[v1].push_back({v2, va});
v[v2].push_back({v1, va});
}
}
}
cout<<bfs(n * m, 0) + 1;
}
