/// (⌐■_■): "who's nvpu, dwuy?"
/// dwuy : "revolym"
#include <bits/stdc++.h>
#define fastIO ios_base::sync_with_stdio(false); cin.tie(NULL)
#define file(a) freopen(a".inp","r",stdin); freopen(a".out", "w",stdout)
#define fi first
#define se second
#define endl "\n"
#define len(s) int32_t(s.length())
#define MASK(k)(1LL<<(k))
#define TASK ""
using namespace std;
typedef tuple<int, int, int> tpiii;
typedef pair<double, double> pdd;
typedef pair<int, int> pii;
typedef long long ll;
const long long OO = 1e18;
const int MOD = 1e9 + 7;
const int INF = 1e9;
const int MX = 4005;
const int dx[] = {0, 0, -1, 1};
const int dy[] = {-1, 1, 0, 0};
int n, m;
string a[MX];
int d[MX][MX];
void nhap(){
cin >> n >> m;
for(int i=0; i<n; i++) cin >> a[i];
}
void solve(){
deque<pii> Q;
d[0][0] = 1;
Q.push_front({0, 0});
int ans = 0;
while(Q.size()){
int x, y;
tie(x, y) = Q.front();
Q.pop_front();
ans = max(ans, d[x][y]);
for(int i=0; i<4; i++){
int u = x + dx[i];
int v = y + dy[i];
if(u<0 || u>=n || v<0 || v>=m || d[u][v]!=0 || a[u][v]=='.') continue;
if(a[u][v] == a[x][y]){
d[u][v] = d[x][y];
Q.push_front({u, v});
}
else{
d[u][v] = d[x][y] + 1;
Q.push_back({u, v});
}
}
}
cout << ans;
}
int32_t main(){
fastIO;
//file(TASK);
nhap();
solve();
return 0;
}
