#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define vll vector<ll>
#define len(x) (ll)x.size()
const ll INF = 1e9, INFL = 1e18;
const ll MOD = 1e9 + 7;
const ll maxn = 5000 + 5;
ll n, m, k = 0;
char a[maxn][maxn];
ll dis[maxn][maxn];
void _() {
cin >> n >> m;
for(ll i = 1; i <= n; i ++){
for(ll j = 1; j <= m; j ++){
cin >> a[i][j];
dis[i][j] = INF;
}
}
deque<pair<ll, ll>>d;
d.push_back({1, 1});
dis[1][1] = 1;
while(!d.empty()){
auto [x, y] = d.front();
d.pop_front();
for(auto [i, j] : vector<pair<ll, ll>>{{x - 1, y}, {x, y - 1}, {x + 1, y}, {x, y + 1}}){
if(i <= 0 or j <= 0 or i > n or j > m) continue;
if(a[i][j] == '.') continue;
if(dis[i][j] > dis[x][y] + (a[x][y] != a[i][j])){
dis[i][j] = dis[x][y] + (a[x][y] != a[i][j]);
if(a[x][y] != a[i][j]) d.push_back({i, j});
else d.push_front({i, j});
}
}
}
ll cv = 0;
for(ll i = 1; i <= n; i ++){
for(ll j = 1; j <= m; j ++){
if(dis[i][j] == INF) continue;
cv = max(cv, dis[i][j]);
}
}
cout << cv << '\n';
}
signed main() {
cin.tie(0)->sync_with_stdio(0);
ll t = 1;
// cin >> t;
while(t --) _();
}
