#include <iostream>
#include <vector>
#include <limits>
#include <map>
#include <algorithm>
#include <set>
#include <string>
#include <cmath>
#include <climits>
#include <string.h>
#include <fstream>
#include <stack>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vb = vector<bool>;
using vvi= vector<vector<int> >;
using vll = vector<long long>;
using vpi = vector<pair<int, int> >;
#define pb push_back
#define rsz resize
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
using pi = pair<int, int>;
#define f first
#define s second
#define mp make_pair
//cin.tie(0)->sync_with_stdio(0);
int H, W;
vector<vector<char> > grid;
vvi depth;
int dx[4]{-1, 1, 0, 0}, dy[4]{0, 0, 1, -1};
int main(){
cin >> H >> W;
grid.rsz(H);
depth.rsz(H);
for (int i = 0; i < H; i++)
{
grid[i].rsz(W);
depth[i].rsz(W);
string str; cin >> str;
for (int j = 0; j < W; j++)
{
grid[i][j] = str[j];
}
}
depth[0][0] = 1;
deque<pair<int, int> > traverse;
traverse.push_front(mp(0, 0));
while(traverse.size() > 0){
pair<int, int> curr = traverse.front(); traverse.pop_front();
for (int i = 0; i < 4; i++)
{
int x = curr.f + dx[i];
int y = curr.s + dy[i];
if(x < 0 || x >= H || y < 0 || y >= W){
continue;
}
if(grid[x][y] == '.' || depth[x][y] != 0){
continue;
}
if(grid[x][y] != grid[curr.f][curr.s]){
depth[x][y] = depth[curr.f][curr.s] + 1;
traverse.push_back(mp(x, y));
} else {
depth[x][y] = depth[curr.f][curr.s];
traverse.push_front(mp(x, y));
}
}
}
int maxV = -1;
for (int i = 0; i < H; i++)
{
for (int j = 0; j < W; j++)
{
maxV = max(depth[i][j], maxV);
}
}
cout << maxV;
}
