#include<bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
signed main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int n,m;cin >> n >> m;
vector<vector<char>> a(n + 1,vector<char> (m + 1));
for(int i = 1;i <= n;i++) for(int j = 1;j <= m;j++) cin >> a[i][j];
auto inside = [&](int i,int j) -> bool{
return i >= 1 && j >= 1 && i <= n && j <= m && a[i][j] != '.';
};
vector<vector<int>> d(n + 1,vector<int> (m + 1));
deque<pair<int,int>> q;
q.push_front({1,1});
d[1][1] = 1;
const int dx[] = {1,-1,0,0};
const int dy[] = {0,0,-1,1};
int ans = 0;
while(!q.empty()){
auto top = q.front();
q.pop_front();
int i = top.F;
int j = top.S;
ans = max(ans,d[i][j]);
for(int t =0 ;t < 4;t++){
int x = i + dx[t];
int y = j + dy[t];
if(inside(x,y) && d[x][y] == 0){
if(a[x][y] == a[i][j]){
d[x][y] = d[i][j];
q.push_front({x,y});
}
else{
d[x][y] = d[i][j] + 1;
q.push_back({x,y});
}
}
}
}
cout << ans << '\n';
}
