#include <bits/stdc++.h>
using namespace std;
#define ull unsigned long long
#define ll long long
#define ld long double
#define pb push_back
#define f first
#define s second
#define sz(x) (int)x.size()
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pld pair<ld,ld>
#define pdd pair<double,double>
#define mp make_pair
#define AmirMakaM ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
//#define int long long
// solve it
const ull SEED = chrono::steady_clock::now().time_since_epoch().count();
mt19937_64 mrand(SEED);
ull rnd(ull x = ~(0ull)) {return mrand() % x;}
const ll MOD = 998244353;
const ll INF = 1e16+20;
const int inf = 1e9 + 7;
const ll N = 1e5+1;
const ll M = 2e3+1;
const double pi = 2*acos(0.0);
const int dx[] = {1,-1,0,0}, dy[] = {0,0,1,-1};
void solve() {
int n, m;
cin >> n >> m;
char a[n+1][m+1];
for(int i=1; i<=n; i++) {
for(int j=1; j<=m; j++) {
cin >> a[i][j];
}
}
int d[n+1][m+1];
for(int i=1; i<=n; i++) {
for(int j=1; j<=m; j++) {
d[i][j] = inf;
}
}
deque<pii> q;
q.push_back({1,1});
d[1][1] = 1;
while(!q.empty()) {
pii cur = q.front();
q.pop_front();
for(int i=0; i<4; i++) {
int x = cur.f + dx[i], y = cur.s + dy[i];
if(!(1<=x&&x<=n&&1<=y&&y<=m&&d[x][y]==inf&&a[x][y]!='.')) continue;
d[x][y] = d[cur.f][cur.s];
if(a[cur.f][cur.s] != a[x][y]) d[x][y]++, q.push_back({x,y});
else q.push_front({x,y});
}
}
int ans = 0;
for(int i=1; i<=n; i++) {
for(int j=1; j<=m; j++) {
if(d[i][j] != inf) ans = max(d[i][j],ans);
}
}
cout << ans;
}
int main() {
AmirMakaM;
srand(SEED);
//freopen("bulk.in", "r", stdin);
//freopen("bulk.out", "w", stdout);
int ttt = 1;
//cin >> ttt;
while(ttt--) {
solve();
}
}
