#include <bits/stdc++.h>
using namespace std;
#define vi(x) vector<x>
#define pb push_back
#define pf push_front
#define FOR(i,a,b) for(int i=a;i<=b;i++)
#define ROF(i,b,a) for(int i=b;i>=a;i--)
#define all(x) begin(x), end(x)
#define sz(x) (int) (x).size()
#define setdecimal(x) cout << fixed << setprecision(x)
using pi = pair<int,int>;
#define f first
#define s second
#define mp make_pair
#define ll long long int
const int N = 4e3+10;
char a[N][N];
int n,m,dis[N][N];
deque<pair<int,int>> dq;
int main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n >> m;
FOR(i,1,n){
FOR(j,1,m){
cin >> a[i][j];
}
}
dq.pb({1,1});
dis[1][1] = 1;
int ans = 1;
while(sz(dq)){
int ni = dq.front().f,nj = dq.front().s;
dq.pop_front();
ans = max(ans,dis[ni][nj]);
FOR(i,-1,1) FOR(j,-1,1) {
if(abs(i) == abs(j)) continue;
int ii = ni+i,jj = nj+j;
if(ii < 1 || ii > n || jj < 1 || jj > m) continue;
if(a[ii][jj] == '.') continue;
if(dis[ii][jj]) continue;
if(a[ii][jj] == a[ni][nj]){
dis[ii][jj] = dis[ni][nj];
dq.pf({ii,jj});
}
else{
dis[ii][jj] = dis[ni][nj]+1;
dq.pb({ii,jj});
}
}
}
cout << ans;
return 0;
}
