#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pii;
typedef vector<ll> vi;
typedef vector<vi> matrix;
#define rep(i, a, b) for(ll i = a; i < b; i++)
#define down(i, b, a) for(ll i = b - 1; i >= a; i--)
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll h, w;
cin >> h >> w;
vector<vector<char>> grid(h, vector<char>(w));
rep(i, 0, h){
rep(j, 0, w){
cin >> grid[i][j];
}
}
matrix dp(h, vi(w, 0));
deque<pii> next;
next.push_front({0, 0});
dp[0][0] = 1;
vi dx = {1, -1, 0, 0};
vi dy = {0, 0, 1, -1};
while(!next.empty()){
pii top = next.front();
next.pop_front();
rep(i, 0, 4){
ll x = top.first + dx[i], y = top.second + dy[i];
if(x < 0 || x >= h || y < 0 || y >= w) continue;
if(dp[x][y]) continue;
if(grid[x][y] == '.') continue;
if(grid[x][y] == grid[top.first][top.second]){
dp[x][y] = dp[top.first][top.second];
next.push_front({x, y});
}
else{
dp[x][y] = dp[top.first][top.second] + 1;
next.push_back({x, y});
}
}
}
ll best = 0;
rep(i, 0, h){
rep(j, 0, w){
best = max(best, dp[i][j]);
}
}
cout << best << endl;
}
