#include <bits/stdc++.h>
using namespace std;
int main() {
cin.tie(0);
ios_base::sync_with_stdio(0);
int h, w;
cin >> h >> w;
vector<string> a(h);
for (int i = 0; i < h; i++){
cin >> a[i];
}
vector<vector<int>> b(h, vector<int>(w));
queue<pair<int, int>> q;
queue<pair<int, int>> p;
q.push({0, 0});
b[0][0]=1;
int x, y;
int s=0;
while(q.size()){
while(q.size()){
x=q.front().first;
y=q.front().second;
q.pop();
if(y-1>=0){
if(b[x][y-1]==0){
if(a[x][y-1]==a[x][y]) {q.push({x, y-1}); b[x][y-1]=1;}
else if(a[x][y-1]!='.') {p.push({x, y-1}); b[x][y-1]=1;}
}
}
if(y+1<w){
if(b[x][y+1]==0){
if(a[x][y+1]==a[x][y]) {q.push({x, y+1}); b[x][y+1]=1;}
else if(a[x][y+1]!='.') {p.push({x, y+1}); b[x][y+1]=1;}
}
}
if(x-1>=0){
if(b[x-1][y]==0){
if(a[x-1][y]==a[x][y]) {q.push({x-1, y}); b[x-1][y]=1;}
else if(a[x-1][y]!='.') {p.push({x-1, y}); b[x-1][y]=1;}
}
}
if(x+1<h){
if(b[x+1][y]==0){
if(a[x+1][y]==a[x][y]) {q.push({x+1, y}); b[x+1][y]=1;}
else if(a[x+1][y]!='.') {p.push({x+1, y}); b[x+1][y]=1;}
}
}
}
swap(q, p);
s++;
}
cout << s;
}
