#include<bits/stdc++.h>
#define IOS ios_base::sync_with_stdio(false);cin.tie();cout.tie();
#define all(x) x.begin(), x.end()
#define int long long
#define pq priority_queue
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define pp pop_back
#define F first
#define S second
using namespace std;
int n, m, ans;
string g[4001];
vector<array<int, 2>> v[2];
int dr[4][2] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
bool c(int x, int y) {
return x >= 0 && y >= 0 && x < n && y < m && g[x][y] != '.';
}
void dfs(int x, int y) {
char t = g[x][y];
g[x][y] = '.';
for (int i = 0; i < 4; i++) {
int X = x + dr[i][0], Y = y + dr[i][1];
if (!c(X, Y)) continue ;
if (g[X][Y] == t) dfs(X, Y);
else v[ans&1^1].pb({X, Y});
}
}
void solve () {
cin >> n >> m;
for (int i = 0; i < n; i++) cin >> g[i];
v[0].pb({0, 0});
for (ans = 0; v[ans&1].size(); ans++) {
for (auto i: v[ans&1]) {
if (c(i[0], i[1])) dfs(i[0], i[1]);
}
v[ans&1].clear();
}
cout << ans;
}
signed main() {IOS solve(); return 0;}
