#include <iostream>
#include <vector>
#include <queue>
using namespace std;
#define pii pair <int, int>
#define pb push_back
#define ff first
#define ss second
int X[] = {-1, 1, 0, 0};
int Y[] = {0, 0, -1, 1};
int main ()
{
ios::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
vector<vector<char>> c(n+1, vector<char>(m+1));
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++) cin >> c[i][j];
}
int ans = 0;
vector<vector<int>> dis(n+1, vector<int>(m+1, 0));
deque<pii> q = {{1, 1}};
dis[1][1] = 1;
while(!q.empty()){
int x = q.front().ff, y = q.front().ss;
q.pop_front();
ans = max(ans, dis[x][y]);
for (int i = 0; i < 4; i++){
int a = x+X[i], b = y+Y[i];
if (a > 0 and b > 0 and a <= n and b <= m and !dis[a][b] and c[a][b] != '.'){
dis[a][b] = dis[x][y];
if (c[x][y] != c[a][b]){
dis[a][b]++;
q.pb({a, b});
}else q.push_front({a, b});
}
}
}
cout << ans << '\n';
}
