#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define ii pair<int,int>
#define vii vector<ii>
#define vi vector<int>
#define fi first
#define se second
#define TASK ""
#define ll long long
#define pll pair<ll, ll>
#define vll vector<ll>
#define vpll vector<pll>
#define pb push_back
#define MASK(i) (1 << (i))
#define BIT(x, i) ((x >> (i)) & 1)
using namespace std;
const int oo = 1e9 + 7;
const ll loo = (ll)1e18 + 7;
const int N = 4e3 + 7;
ll n, m, dist[N][N];
char a[N][N];
bool visited[N][N];
const int dx[4] = {-1, 1, 0, 0};
const int dy[4] = {0, 0, -1, 1};
bool check(ll i, ll j){
if (i < 1 || j < 1 || i > n || j > m || a[i][j] == '.' || visited[i][j]) return false;
return true;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
//freopen(TASK".in", "r", stdin);
//freopen(TASK".out", "w", stdout);
cin >> n >> m;
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++){
cin >> a[i][j];
}
}
deque<pll> kew;
kew.push_back({1, 1});
visited[1][1] = true;
ll res = 0;
while (!kew.empty()){
auto k = kew.front();
kew.pop_front();
res = max(res, dist[k.fi][k.se]);
for (int i = 0; i < 4; i++){
ll newx = k.fi + dx[i];
ll newy = k.se + dy[i];
if (check(newx, newy)){
visited[newx][newy] = true;
dist[newx][newy] = dist[k.fi][k.se];
if (a[k.fi][k.se] == a[newx][newy]){
kew.push_front({newx, newy});
}
else {
dist[newx][newy]++;
kew.push_back({newx, newy});
}
}
}
}
cout << res + 1;
return 0;
}
