#include "bits/stdc++.h"
using namespace std;
/*
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using ordered_set = tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>;
*/
#define all(x) begin(x), end(x)
#define sz(x) (int)x.size()
using ll = long long;
const int mod = 1e9+7;
vector<string> v;
int n, m;
int ans = 0;
array<vector<array<int, 2>>, 2> cur;
bool isValid(int i, int j) {
return i < n and i >= 0 and j < m and j >= 0 and v[i][j] != '.';
}
vector<array<int, 2>> moves = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
void dfs(array<int, 2> a) {
char c = v[a[0]][a[1]];
v[a[0]][a[1]] = '.';
for (auto m : moves) {
int nx = a[0] + m[0], ny = a[1] + m[1];
if (isValid(nx, ny)) {
if (v[nx][ny] == c) {
dfs({nx, ny});
} else {
cur[ans&1?0:1].push_back({nx, ny});
}
}
}
}
void solve(int tc) {
cin >> n >> m;
v.resize(n);
for (auto &x : v) cin >> x;
cur[0].push_back({0, 0});
while (!cur[ans&1].empty()) {
for (auto x : cur[ans&1]) {
if (isValid(x[0], x[1])) {
dfs(x);
}
}
cur[ans&1].clear();
++ans;
}
cout << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(false); cin.tie(NULL);
int tc = 1;
//cin >> tc;
for (int i = 1; i <= tc; ++i) solve(i);
return 0;
}
