#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define ull unsigned long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second
const int N = 4e3 + 5;
const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
queue<pair<int, int>> q1, q2;
char a[N][N];
bool vis[N][N];
int main() {
ios_base::sync_with_stdio(false); cin.tie(NULL);
int h, w, cnt = 0, ans = 0;
cin >> h >> w;
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
cin >> a[i][j];
if (a[i][j] != '.') cnt++;
}
}
q1.push({1, 1});
vis[1][1] = 1, cnt--;
while (cnt > 0) {
ans++;
while (!q1.empty()) {
int x = q1.front().fi, y = q1.front().se;
q1.pop();
cnt--;
for (int i = 0; i < 4; i++) {
int tx = x + dx[i], ty = y + dy[i];
if (tx < 1 or ty < 1 or tx > h or ty > w or vis[tx][ty] or a[tx][ty] == '.') continue;
else if (a[x][y] == a[tx][ty]) vis[tx][ty] = 1, q1.push({tx, ty});
else vis[tx][ty] = 1, q2.push({tx, ty});
}
}
q1 = q2;
while (!q2.empty()) q2.pop();
}
cout << ans << "\n";
}
