#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fore(i, a, b) for (int i = (a), _b = (b); i < _b; ++i)
#define fort(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define fordt(i, a, b) for (int i = (a), _b = (b); i >= _b; --i)
#define forde(i, a, b) for (int i = (a), _b = (b); i > _b; --i)
#define trav(a, x) for (auto& a : x)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
using namespace std;
using namespace __gnu_pbds;
template<class A, class B> bool maxi(A &a, const B &b) {return (a < b) ? (a = b, true):false;};
template<class A, class B> bool mini(A &a, const B &b) {return (a > b) ? (a = b, true):false;};
typedef int64_t i64;
typedef pair<int,int> _ii;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
constexpr int maxn=2e5+7;
constexpr i64 oo=1e9+7;
const int dx[] = {-1, 1, 0, 0};
const int dy[] = {0, 0, -1, 1};
char c[4007][4007];
int n, m, dp[4007][4007];
bool in(int x, int y) {
return x >= 1 && x <= n && y >= 1 && y <= m && c[x][y] != '.';
}
struct Node {
int x, y, val;
Node(int x, int y, int val): x(x), y(y), val(val) {}
};
void solve() {
cin >> n >> m;
deque <Node> dq;
fort(i, 1, n) fort(j, 1, m) {
dp[i][j] = oo;
cin >> c[i][j];
}
dq.push_back({1, 1, 1});
dp[1][1] = 1;
while(dq.size()) {
auto [x, y, val] = dq.front(); dq.pop_front();
if(val > dp[x][y]) continue;
fore(i, 0, 4) {
int nX = x + dx[i], nY = y + dy[i];
if(!in(nX, nY)) continue;
int cost = (c[nX][nY] != c[x][y] ? 1 : 0);
if(dp[nX][nY] > dp[x][y] + cost) {
dp[nX][nY] = dp[x][y] + cost;
if(cost) dq.push_back(Node(nX, nY, dp[nX][nY]));
else dq.push_front(Node(nX, nY, dp[nX][nY]));
// cout << x << " " << y << " : " << nX << " " << nY << " - " << cost << endl;
// cout << dp[x][y] << " --- " << dp[nX][nY] << endl;
}
}
}
int ans = 0;
fort(i, 1, n) fort(j, 1, m) {
if(dp[i][j] < oo) maxi(ans, dp[i][j]);
}
cout << ans;
}
#define NAME "test."
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
if(fopen(NAME"inp", "r")) {
freopen(NAME"inp", "r", stdin);
freopen(NAME"out", "w", stdout);
}
int t=1;
while(t--) solve();
}
