#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize ("Ofast")
#define all(x) x.begin() , x.end()
#define sze(x) (ll)(x.size())
#define mp(x , y) make_pair(x , y)
#define wall cout<<"--------------------------------------\n";
typedef long long int ll;
typedef pair<ll , ll> pll;
typedef pair<int , int> pii;
typedef double db;
typedef pair<pll , ll> plll;
typedef pair<int , pii> piii;
typedef pair<pll , pll> pllll;
const ll maxn = 4e3 + 17 , maxv = 16e6 + 17 , md = 1e9 + 7 , inf = 2e16;
vector<int> adj[maxv][2] , f , g;
char a[maxn][maxn];
bool mark[maxv];
int main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int n , m;
cin>>n>>m;
for(int i = 0 ; i < n ; i++){
for(int j = 0 ; j < m ; j++){
cin>>a[i][j];
}
}
for(int i = 0 ; i < n ; i++){
for(int j = 0 ; j < m ; j++){
int v = i * m + j;
if(i > 0){
if(a[i - 1][j] != '.'){
adj[v][a[i - 1][j] != a[0][0]].push_back(v - m);
}
}
if(j > 0){
if(a[i][j - 1] != '.'){
adj[v][a[i][j - 1] != a[0][0]].push_back(v - 1);
}
}
if(i < n - 1){
if(a[i + 1][j] != '.'){
adj[v][a[i + 1][j] != a[0][0]].push_back(v + m);
}
}
if(j < m - 1){
if(a[i][j + 1] != '.'){
adj[v][a[i][j + 1] != a[0][0]].push_back(v + 1);
}
}
}
}
int lm = n * m - 1;
mark[0] = mark[lm] = true;
f.push_back(0); f.push_back(lm);
g.push_back(0); g.push_back(lm);
int ans;
for(int j = 0 ; ; j++){
if(f.empty()){
ans = j - 1;
break;
}
int x = 0;
while(x < sze(f)){
int v = f[x++];
for(auto i : adj[v][j & 1]){
if(mark[i]) continue;
mark[i] = true;
f.push_back(i);
g.push_back(i);
}
}
f = g;
g.clear();
}
cout<<ans<<'\n';
return 0;
}
