#include<bits/stdc++.h>
typedef long long ll;
#define int long long
#define pii pair<ll, ll>
#define fi first
#define se second
#define endl '\n'
#define TASK ""
#define N 4005
#define LOG 16
using namespace std;
bool ghuy4g;
const ll hx[] = {-1, 0, 1, 0};
const ll hy[] = {0, 1, 0, -1};
ll n, m, tong;
char a[N][N];
ll idx[N][N], cur, par[N * N];
bool vst[N * N];
pii p[N * N];
vector<ll> vt[N * N];
ll find(ll u) {
if (par[u] < 0) return u;
return par[u] = find(par[u]);
}
void join(ll u, ll v) {
u = find(u);
v = find(v);
if (u == v) return;
if (par[u] <= par[v]) {
par[u] += par[v];
par[v] = u;
}
else {
par[v] += par[u];
par[u] = v;
}
}
void solve() {
ll ans = 0;
vector<ll> nxt;
nxt.push_back(find(idx[n][m]));
vector<ll> cur = nxt;
nxt.clear();
while (true) {
if (cur.size() == 0) break;
ans ++ ;
for (auto u : cur) {
for (auto it : vt[u]) {
vst[it] = 1;
for (int z = 0; z < 4; z ++) {
ll dx = p[it].fi + hx[z];
ll dy = p[it].se + hy[z];
if (dx < 1 || dy < 1 || dx > n || dy > m) continue;
if (a[dx][dy] == a[p[it].fi][p[it].se] || a[dx][dy] == '.') continue; // cung ma ke => cung tplt
ll root = find(idx[dx][dy]);
if (vst[root] == 0) {
vst[root] = 1;
nxt.push_back(root);
}
}
}
}
cur = nxt;
nxt.clear();
}
cout << ans << endl;
}
void pre() {
for (int i = 1; i <= cur; i ++) par[i] = -1;
for (int i = 1; i <= n; i ++) {
for (int j = 1; j <= m; j ++) {
if (a[i][j] == '.') continue;
for (int z = 0; z < 4; z ++) {
ll dx = i + hx[z], dy = j + hy[z];
if (dx < 1 || dy < 1 || dx > n || dy > m) continue;
if (a[dx][dy] != a[i][j]) continue;
join(idx[dx][dy], idx[i][j]);
}
}
}
for (int i = 1; i <= n; i ++) {
for (int j = 1; j <= m; j ++) {
if (a[i][j] == '.') continue;
ll root = find(idx[i][j]);
vt[root].push_back(idx[i][j]);
}
}
}
bool klinh;
signed main() {
// freopen("test.inp", "r", stdin);
//freopen("test.out", "w", stdout);
//srand(time(0));
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for (int i = 1; i <= n; i ++) {
for (int j = 1; j <= m; j ++) {
cin >> a[i][j];
if (a[i][j] != '.') {
tong ++ ;
idx[i][j] = ++ cur;
p[cur] = {i, j};
}
}
}
pre();
solve();
cerr << fabs(&klinh - &ghuy4g) / double(1024 * 1024);
}
