#include <bits/stdc++.h>
using namespace std;
#define pii pair <int, int>
#define ff first
#define ss second
const int N = 4001;
int n, m, ans = 0;
char c[N][N];
bool vis[N][N];
int X[] = {-1, 1, 0, 0};
int Y[] = {0, 0, -1, 1};
int main ()
{
ios::sync_with_stdio(false);
cin.tie(0);
cin >> n >> m;
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++) cin >> c[i][j];
}
priority_queue<pair<int,pii>> q;
q.push({-1, {1, 1}});
vis[1][1] = 1;
while(!q.empty()){
int x = q.top().ss.ff, y = q.top().ss.ss, w = q.top().ff;
q.pop();
ans = max(ans, -w);
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 !vis[a][b] and c[a][b] != '.'){
vis[a][b] = 1;
if (c[x][y] != c[a][b]) q.push({w-1, {a, b}});
else q.push({w, {a, b}});
}
}
}
cout << ans << '\n';
}
