#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 4000;
const int inf = 1e9;
const int dx[] = {0,0,-1,1};
const int dy[] = {-1,1,0,0};
struct node{
int x,y,w;
};
int n, m;
char a[N+5][N+5];
int d[N+5][N+5];
bool chk(int x,int y){
return (1 <= x && x <= n && 1 <= y && y <= m && a[x][y] != '.');
}
int main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin >> n >> m;
for(int i = 1 ; i <= n ; ++i)
for(int j = 1 ; j <= m ; ++j){
cin >> a[i][j];
d[i][j] = inf;
}
deque<node> Deque;
Deque.push_back({1,1,1});
d[1][1] = 1;
while(!Deque.empty()){
node t = Deque.front();
Deque.pop_front();
int x = t.x;
int y = t.y;
int w = t.w;
if(w > d[x][y]) continue;
//cout << x <<' ' << y << ' ' <<w << '\n';
for(int j = 0 ; j < 4 ; ++j){
int _x = x + dx[j];
int _y = y + dy[j];
if(!chk(_x,_y)) continue;
int _w = w + (a[_x][_y] != a[x][y]);
//cout << _x << '.' << _y <<' ' <<_w << '\n';
if(_w < d[_x][_y]){
d[_x][_y] = _w;
if(_w > w) Deque.push_back({_x,_y,_w});
else Deque.push_front({_x,_y,w});
}
}
}
int mx = 0;
for(int i = 1 ; i <= n ; ++i)
for(int j = 1 ; j <= m ; ++j)
if(a[i][j] != '.')
mx = max(mx,d[i][j]);
cout << mx;
return 0;
}
