#include<bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
#define watch(x) cerr << "\n" << (#x) << " is " << (x) << "\n";
#define int long long
#define ffor(i, a, b) for(int i=a;i<b;i++)
#define rfor(i, a, b) for(int i=a-1;i>=b;i--)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define pb push_back
#define fi first
#define se second
#define pii pair<int, int>
#define vi vector<int>
#define vvi vector<vi>
#define show(a) for(auto e : a) {cout<<e<<" ";} cout<<"\n";
#define pr(a, b, c) ffor(i, b, c) {cout<<a[i]<<" ";} cout<<"\n";
#define cerr if(false)cerr
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int N = 2e5 + 10;
int Mod = 1e9 + 7, INF = 1e18, BASE = 7, Block = 555;
void solve() {
int n, m; cin>>n>>m;
int x[4] = {1, -1, 0, 0};
int y[4] = {0, 0, 1, -1};
char a[n][m];
ffor(i, 0, n) {
ffor(j, 0, m) cin>>a[i][j];
}
deque<array<int, 2>> q;
q.push_back({0, 0});
int vis[n][m];
memset(vis, 0x3f, sizeof(vis));
vis[0][0] = 1;
while(q.size()) {
auto v = q.front(); q.pop_front();
ffor(i, 0, 4) {
int nx = v[0] + x[i];
int ny = v[1] + y[i];
if(!(nx >= 0 && nx < n && ny >= 0 && ny < m) || a[nx][ny] == '.') continue;
int w = a[nx][ny] != a[v[0]][v[1]];
if(vis[nx][ny] > vis[v[0]][v[1]] + w) {
vis[nx][ny] = vis[v[0]][v[1]] + w;
if(w == 0) q.push_front({nx, ny});
else q.push_back({nx, ny});
}
}
}
int ans = 0;
ffor(i, 0, n) {
ffor(j, 0, m) if(a[i][j]!='.') {ans = max(ans, vis[i][j]); }
}
cout<<ans<<"\n";
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int t = 1; //cin>>t;
while(t--) solve();
return 0;
}
