#include<bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for(int i = (a); i<=(b); ++i)
#define REPD(i,a,b) for(int i = (a); i>=(b); --i)
#define REPDIS(i,a,b,c) for(int i = (a); i<=(b); i += c)
#define task "test"
#define task1 "nnhzzz"
#define ALL(x) (x).begin(),(x).end()
#define SZ(x) (int)(x).size()
#define MASK(x) (1LL<<x)
#define BIT(x,i) ((x>>i)&1LL)
#define vi vector<int>
#define vvi vector<vi>
#define pii pair<int,int>
#define vpii vector<pii>
#define fi first
#define se second
#define ld long double
#define ll long long
//-------------------------------------------------------------------------------//
template<typename T> bool mini(T &a, T b){if(a>b){a=b;return true;}return false;}
template<typename T> bool maxi(T &a, T b){if(a<b){a=b;return true;}return false;}
//-------------------------------------------------------------------------------//
const int MAXN = 4e3+7,N = 1e5+7,inf = 1e9,LOG = 20;
const int MOD = 1e9+7,MOD1 = 123456789;
const int dx[] = {1,0,0,-1};
const int dy[] = {0,1,-1,0};
//-------------------------------------------------------------------------------//
char c[MAXN][MAXN];
int d[MAXN][MAXN];
int n,m,res = 1;
bool ok(int x, int y){
return (x>=1 && y>=1 && x<=n && y<=m);
}
void solve(){
cin >> n >> m;
REP(i,1,n) REP(j,1,m) cin >> c[i][j];
deque<pii> q; d[1][1] = 1;
q.emplace_back(1,1);
while(SZ(q)!=0){
int x = q.front().fi,y = q.front().se; q.pop_front();
REP(i,0,3){
int nx = x+dx[i],ny = y+dy[i];
if(ok(nx,ny)==false || c[nx][ny]=='.' || d[nx][ny]!=0) continue;
if(c[x][y]==c[nx][ny]){
d[nx][ny] = d[x][y];
q.emplace_front(nx,ny);
}else{
maxi(res,d[x][y]+1);
d[nx][ny] = d[x][y]+1;
q.emplace_back(nx,ny);
}
}
}
cout << res;
}
signed main(){
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
if(fopen(task".inp","r")){
freopen(task".inp","r",stdin);
freopen(task".out","w",stdout);
}
if(fopen(task1".inp","r")){
freopen(task1".inp","r",stdin);
freopen(task1".out","w",stdout);
}
solve();
return 0;
}
