#include <bits/stdc++.h>
using namespace std;
// ---------- debug utilities ----------
#ifndef Local
#define debug(...)
#define debugArr(...)
#else
#include <debug.cpp>
auto start = chrono::high_resolution_clock::now();
#endif
// ---------- shortcut macros ----------
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define len(x) (int)(x).size()
#define pb push_back
#define print1(zzz) for(auto zzzz: zzz) cout << zzzz << ' ';cout<<endl;
#define print2(zzz) for (auto &zzzzz : zzz) {print1(zzzzz)}
#define space cout << endl;
#define sum(v) (accumulate((v).begin(), (v).end(), 0LL))
#define lb(v, x) (lower_bound((v).begin(), (v).end(), (x)) - (v).begin())
#define ub(v, x) (upper_bound((v).begin(), (v).end(), (x)) - (v).begin())
#define execute ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
// ----------- constants -----------
#define PI 3.14159265358979323846
#define INF 1e18
#define MOD 1000000007
#define MOD2 998244353
// ---------- type aliases ----------
#define ll long long
#define int long long
#define vi vector<int>
#define vc vector<char>
#define vs vector<string>
#define vvc vector<vector<char>>
#define vvi vector<vector<int>>
#define pii pair<int, int>
// ---------- input macros ----------
#define msb(x) (x == 0 ? -1 : 1ll<<(63 - __builtin_clzll(x)))
#define lsb(x) (x == 0 ? -1 : 1ll<<(__builtin_ctzll(x)))
#define pc(x) (__builtin_popcountll(x))
ll gcd(ll a, ll b) {return b ? gcd(b, a % b) : a;}
ll lcm(ll a, ll b) {return a * b / gcd(a, b);}
int h, w;
vvc med;
void solve() {
cin >> h >> w;
med.assign(h, vector<char>(w));
vector<vector<int>> vis(h, vector<int>(w, 1e9));
for (int i=0; i<h; i++) {
for (int j=0; j<w; j++) {
cin >> med[i][j];
}
}
deque<array<int,3>> qu;
qu.push_back({0,0,0});
vis[0][0] = 0;
int dx[4] = {0,0,1,-1};
int dy[4] = {1,-1,0,0};
while (!qu.empty()) {
auto [x,y,c] = qu.front();
qu.pop_front();
for (int i=0; i<4; i++) {
int nx = x+dx[i];
int ny = y+dy[i];
if (nx<0 || nx>=h || ny<0 || ny>=w) continue;
if (med[nx][ny]=='.') continue;
int nc = c + (med[x][y] != med[nx][ny]);
if (vis[nx][ny] > nc) {
vis[nx][ny] = nc;
if (med[x][y] == med[nx][ny])
qu.push_front({nx,ny,nc});
else
qu.push_back({nx,ny,nc});
}
}
}
int ans = 0;
for (int i=0; i<h; i++) {
for (int j=0; j<w; j++) {
if (med[i][j] == '.') continue;
ans = max(ans, vis[i][j]);
}
}
cout << ans+1;
}
int32_t main(){
// cout << fixed << setprecision(10);
#ifdef Local
// freopen("input.txt", "r+", stdin);
// freopen("output.txt", "w+", stdout);
#endif
execute
int t = 1;
// cin >> t;
while (t--) {
solve();
}
#ifdef Local
chrono::duration<double> elapsed = chrono::high_resolution_clock::now() - start;
cerr << fixed << setprecision(6) << "\nTime: " << elapsed.count() << "s\n";
#endif
return 0;
}
