#include <bits/stdc++.h>
#define ll long long
using namespace std;
typedef vector<int> vi;
typedef pair<int,int> pi;
const int INF = 1e9;
const int MX = 5e5 + 23;
const int MOD = 1e9+7;
const int MAX_N = 1e6;
const int MAX_N2 = 1e5;
const int TWO_MOD_INV = 500000004;
const int M = 998244353;
int depth[4000][4000], dx[4]={1, -1, 0, 0}, h,w, dy[4]={0, 0, 1, -1};
char grid[4000][4000];
bool inside(int x, int y) {
if(x>=0 && y>=0 && x<h && y<w && grid[x][y]!='.') return 1;
return 0;
}
void solve() {
cin >> h >> w;
for(int i=0; i<h; ++i) {
string s;
cin >> s;
for(int j=0; j<w; ++j) {
grid[i][j]=s[j];
}
}
deque<pair<int,int>>q;
q.push_back({0, 0});
int ans=0;
memset(depth, 0, sizeof depth);
depth[0][0]=1;
while(!q.empty()) {
pair<int,int>c=q.front();
q.pop_front();
ans=max(ans, depth[c.first][c.second]);
for(int i=0; i<4; ++i) {
int x=c.first+dx[i], y=c.second+dy[i];
if(!inside(x,y) or depth[x][y]) continue;
if(grid[x][y]==grid[c.first][c.second]) {
depth[x][y]=depth[c.first][c.second];
q.push_front({x,y});
} else {
depth[x][y]=depth[c.first][c.second]+1;
q.push_back({x, y});
}
}
}
cout << ans << endl;
}
signed main()
{
//freopen("odometer.in","r",stdin);
//freopen("odometer.out","w",stdout);
int t=1;
while(t--) solve();
return 0;
}
