#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define ar array
#define fi first
#define se second
#define ii pair <int, int>
#define vt vector
#define pb push_back
#define sz(x) (int)(x).size()
#define reset(a, x) memset(a, x, sizeof(a))
#define u128 __uint128_t
#define F_OR(i, a, b, s) for (int i=(a); (s)>0?i<=(b):i>=(b); i+=(s))
#define F_OR1(e) F_OR(i, 0, (e)-1, 1)
#define F_OR2(i, e) F_OR(i, 0, (e)-1, 1)
#define F_OR3(i, b, e) F_OR(i, (b), (e), 1)
#define F_OR4(i, b, e, s) F_OR(i, (b), (e), (s))
#define GET5(a, b, c, d, e, ...) e
#define F_ORC(...) GET5(__VA_ARGS__, F_OR4, F_OR3, F_OR2, F_OR1)
#define fo(...) F_ORC(__VA_ARGS__)(__VA_ARGS__)
#define each(x, a) for (auto& x: a)
#define END cerr << "\n";
#define error(args...) { \
string _s = #args; \
replace(_s.begin(), _s.end(), ',', ' '); \
stringstream _ss(_s); \
istream_iterator <string> _it(_ss); \
err(_it, args); \
}
void err(istream_iterator<string> it) {}
template<typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
cerr << *it << "=" << a << ", ";
err(++it, args...);
}
template<class T> void read(T& x) {
cin >> x;
}
template<class H, class... T> void read(H& h, T&... t) {
read(h);
read(t...);
}
template<class A> void write(A x) {
cout << x;
}
template<class H, class... T> void write(const H& h, const T&... t) {
write(h);
write(t...);
}
void print() {
write("\n");
}
template<class H, class... T> void print(const H& h, const T&... t) {
write(h);
if(sizeof...(t))
write(' ');
print(t...);
}
#define file ""
//#define int ll
const long long INF = 2e18;
const int inf = 0x3c3c3c3c, N = 4e3;
int h, w, d[N][N];
deque <ii> dq;
string grid[N];
inline bool ok(int x, int y) {
return (min(x, y) >= 0 && x < h && y < w && grid[x][y] != '.');
}
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};
void solve() {
read(h, w);
fo(h) read(grid[i]);
reset(d, inf);
d[0][0] = 1;
dq.pb({0, 0});
while (sz(dq)) {
ii u = dq.front();
dq.pop_front();
fo(4) {
int newx = u.fi+dx[i];
int newy = u.se+dy[i];
if (!ok(newx, newy)) continue;
int cost = grid[u.fi][u.se] != grid[newx][newy];
if (d[newx][newy] > d[u.fi][u.se]+cost) {
d[newx][newy] = d[u.fi][u.se]+cost;
if (cost) dq.pb({newx, newy});
else dq.push_front({newx, newy});
}
}
}
int ans = 0;
fo(x, h) fo(y, w) if (ok(x, y)) ans = max(ans, d[x][y]);
write(ans);
}
int32_t main() {
//freopen(file".out", "w", stdout); freopen(file".in", "r", stdin);
cin.tie(0)->sync_with_stdio(0);
int Case = 1;
//read(Case);
fo(ttest, 1, Case) {
//write("Case ", ttest, ": ");
solve();
}
}
