#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define ld long double
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define all(a) a.begin(), a.end()
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
char M[4001][4001];
int dist[4001][4001];
int main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int H, W; cin >> H >> W;
for(int i = 1; i <= H; ++i){
for(int j = 1; j <= W; ++j){
cin >> M[i][j];
dist[i][j] = 1e9;
}
}
deque<pair<int, int>> dq;
dq.push_front({1, 1});
dist[1][1] = 1;
int answer = 1;
while(!dq.empty()){
int x, y; tie(x, y) = dq.front(); dq.pop_front();
for(int k = 0; k < 4; ++k){
int nx = x + dx[k], ny = y + dy[k];
if(nx > 0 && ny > 0 && nx <= H && ny <= W && dist[nx][ny] == 1e9 && M[nx][ny] != '.'){
dist[nx][ny] = dist[x][y];
if(M[x][y] != M[nx][ny]){
dist[nx][ny]++;
dq.push_back({nx, ny});
}
else{
dq.push_front({nx, ny});
}
answer = max(answer, dist[nx][ny]);
}
}
}
cout << answer;
return 0;
}
