#include <iostream>
#include <tuple>
#include <set>
#include <map>
#include <bitset>
#include <vector>
#include <queue>
#include <cstring>
#include <stack>
#include <stdio.h>
#include <algorithm>
#include <math.h>
#include <climits>
#include <unordered_map>
#include <unordered_set>
#include <cstdint>
#include <chrono>
#include <thread>
#include <omp.h>
#include <iomanip>
#include <numeric>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define fastIO ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
#define pb push_back
#define mp make_pair
#define f first
#define s second
#define sz(a) (int)a.size()
#define all(a) (a).begin(), (a).end()
#define md(a, b) ((a) % b + b) % b
#define MOD(a) md(a, MOD)
#define mem(a, h) memset(a, (h), sizeof(a))
#define forn(i, n) for (int i = 0; i < n; i++)
#define fore(i, b, e) for (int i = b; i < e; i++)
#define forev(i, e, b) for (int i = e; i > b; i--)
#define DBG(x) cerr<<#x<<" = "<<(x)<<endl
#define UNIQUE(x) (x).resize(unique(all(x)) - (x).begin())
#define RAYA cout<<"=============================="<<'\n'
#define yes cout << "YES" << endl;
#define no cout << "NO" << endl;
#define PI acos(-1)
template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename T>
istream &operator>>(istream &in, vector<T> &a) {
for (auto &x : a) in >> x;
return in;
}
template <typename T>
ostream &operator<<(ostream &out, vector<T> &a) {
for (auto &x : a) out << x << " ";
return out;
}
typedef long long ll;
typedef pair<ll, ll> pll;
typedef vector<ll> vll;
const int MOD = int(1e9) + 7;
ll mod(ll a) {return a >= MOD ? a - MOD : a;}
ll mod_mul(ll a, ll b) {return mod(a * b);}
ll mod_add(ll a, ll b) {return mod(a + b);}
ll gcd(ll a, ll b) { if (b == 0) return a; return gcd(b, a % b);}
ll lcm(ll a, ll b) {return (a * b) / gcd(a, b);}
ll exp(ll x, ll n) { if (n == 0) return 1; ll u = exp(x, n / 2); u = (u * u); if (n % 2 == 1) u = (u * x); return u; }
ll expmod(ll x, ll n) {if (n == 0) return 1 % MOD; ll u = expmod(x, n / 2); u = (u * u) % MOD; if (n & 1) u = (u * x) % MOD; return u; }
ll invmod(ll a){ return expmod(a, MOD - 2); }
int dx[4]{1, 0, -1, 0}, dy[4]{0, 1, 0, -1};
ll n, m;
vector<string> grid;
bool inside(ll x, ll y) {
return x >= 0 && y >= 0 && x < n && y < m && grid[x][y] != '.';
}
void solve() {
cin >> n >> m;
grid.resize(n);
forn (i, n) cin >> grid[i];
vector<vector<ll>> depth(n, vll(m));
depth[0][0] = 1;
deque<pll> q;
q.pb({0, 0});
ll ans = 0;
while (q.size()) {
auto v = q.front(); q.pop_front();
ans = max(ans, depth[v.f][v.s]);
forn (i, 4) {
ll x = v.f + dx[i], y = v.s + dy[i];
if (inside(x, y) && depth[x][y] == 0) {
if (grid[x][y] == grid[v.f][v.s]) {
depth[x][y] = depth[v.f][v.s];
q.push_front({x, y});
} else {
depth[x][y] = depth[v.f][v.s] + 1;
q.push_back({x, y});
}
}
}
}
cout << ans << '\n';
}
int main() {
fastIO;
// cout << fixed;
// cout << setprecision(10);
// neighbors.assign(n, vll());
int t = 1;
// cin >> t;
while (t--) solve();
return 0;
}
