#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <math.h>
#include <set>
#include <map>
#include <string>
#include <tuple>
#include <numeric>
#include <climits>
#include <bitset>
#include <iomanip>
#include <random>
#include <ctime>
using namespace std;
typedef int ll;
ll max(ll a, ll b) {
if (a > b) {
return a;
} else {
return b;
}
}
ll min(ll a, ll b) {
if (a < b) {
return a;
} else {
return b;
}
}
const ll MAXN = 4001;
const ll MAXM = 2097153;
const ll MOD = 1e9 + 7;
const ll INF = 1e7;
ll dr[4] = {0, 1, 0, -1};
ll dc[4] = {1, 0, -1, 0};
void solve(ll ca) {
ll h, w;
cin >> h >> w;
char grid[h][w];
for (ll i = 0; i < h; i++) {
for (ll j = 0; j < w; j++) {
cin >> grid[i][j];
}
}
ll cheapest[h][w];
for (ll i = 0; i < h; i++) {
for (ll j = 0; j < w; j++) {
cheapest[i][j] = INF;
}
}
deque<pair<ll, ll>> dq1;
deque<ll> dq2;
dq1.push_back({0, 0});
dq2.push_back(0);
ll ans = 0;
while (!dq1.empty()) {
pair<ll, ll> cur = dq1.front();
ll cos = dq2.front();
dq1.pop_front();
dq2.pop_front();
if (cheapest[cur.first][cur.second] != INF) {
continue;
}
ans = max(ans, cos);
cheapest[cur.first][cur.second] = cos;
for (ll k = 0; k < 4; k++) {
ll nr = cur.first + dr[k];
ll nc = cur.second + dc[k];
if (nr >= 0 && nr < h && nc >= 0 && nc < w && cheapest[nr][nc] == INF && grid[nr][nc] != '.') {
if (grid[nr][nc] == grid[cur.first][cur.second]) {
dq1.push_front({nr, nc});
dq2.push_front(cos);
} else {
dq1.push_back({nr, nc});
dq2.push_back(cos+1);
}
}
}
}
cout << ans+1 << endl;
}
int main() {
mt19937 rng(0);
// Fast IO
ios::sync_with_stdio(false);
cin.tie(nullptr);
/*
freopen("piggyback.in", "r", stdin);
freopen("piggyback.out", "w", stdout);
*/
ll t = 1;
//cin >> t;
ll co = 0;
while (t--) {
solve(co);
co++;
}
}
