#include <bits/stdc++.h>
#include <functional>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define ll long long
#define pii pair<ll,ll>
#define fi first
#define sec second
#define double long double
#define debug(x) cout << #x << " = " << x << "\n";
const ll MOD = 1e9 + 7;
const ll N = 1e6 + 5;
const ll INF = 1e18;
template <typename T>
ostream& operator << (ostream& os, vector<T>tmp){
os << "[";
for(auto x : tmp) os << " " << x;
os << " ]";
return os;
}
template <typename T>
ostream& operator << (ostream& os, set<T>tmp){
os << "[";
for(auto x : tmp) os << " " << x;
os << " ]";
return os;
}
ll a[N];
ostream& operator << (ostream& os, pii x){
os << "[";
os << " " << x.fi << " " << x.sec;
os << " ]";
return os;
}
int32_t main(){
cin.tie(0)->sync_with_stdio(0);
int tc = 1;
// cin >> tc;
for(;tc--;){
ll h,w; cin >> h >> w;
char grid[h + 5][w + 5];
ll dist[h + 5][w + 5];
memset(dist, 0x3f, sizeof(dist));
dist[1][1] = 1;
for(int i=1;i<=h;i++){
for(int j=1;j<=w;j++) cin >> grid[i][j];
}
deque<pair<ll, pii>>dq;
dq.push_back({1, {1, 1}});
ll di[] = {0, 0, 1, -1}, dj[] = {1, -1, 0, 0};
for(;!dq.empty();){
auto x = dq.front(); dq.pop_front();
if(x.fi > dist[x.sec.fi][x.sec.sec]) continue;
for(int i=0;i<4;i++){
ll newi = x.sec.fi + di[i], newj = x.sec.sec + dj[i];
if(newi < 1 || newj < 1 || newi > h || newj > w) continue;
if(grid[newi][newj] == '.' || dist[newi][newj] <= x.fi + (grid[newi][newj] != grid[x.sec.fi][x.sec.sec])) continue;
dist[newi][newj] = x.fi + (grid[newi][newj] != grid[x.sec.fi][x.sec.sec]);
if(grid[newi][newj] != grid[x.sec.fi][x.sec.sec]) dq.push_back({dist[newi][newj], {newi, newj}});
else dq.push_front({dist[newi][newj], {newi, newj}});
}
}
ll mx = 1;
for(int i=1;i<=h;i++){
for(int j=1;j<=w;j++){
if(grid[i][j] != '.') mx = max(mx, dist[i][j]);
}
}
cout << mx << "\n";
}
}
/*
*/
