#include "bits/stdc++.h"
#define sz(x) (int)size(x)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
using namespace std;
using ll = long long;
using pii = pair<int, int>;
const char nl = '\n';
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3f;
int dx[] = {0, 0, 1, -1};
int dy[] = {-1, 1, 0, 0};
int32_t main() {
ios::sync_with_stdio(0), cin.tie(0);
int n, m; cin >> n >> m;
vector<string> ma(n); for (auto &x : ma) cin >> x;
vector d(n, vector<int>(m, INF));
deque<pii> q;
q.push_front({0, 0});
d[0][0] = 1;
auto val = [&](int i, int j) -> bool {
return 0 <= i && i < n && 0 <= j && j < m && ma[i][j] != '.';
};
int ans = 1;
while (!q.empty()) {
auto [x, y] = q.front(); q.pop_front();
ans = max(ans, d[x][y]);
for (int i = 0; i < 4; i++) {
int nx = x + dx[i];
int ny = y + dy[i];
if (!val(nx, ny)) continue;
int w = (ma[x][y] != ma[nx][ny]);
if (d[x][y] + w < d[nx][ny]) {
d[nx][ny] = d[x][y] + w;
if (w == 0)
q.push_front({nx, ny});
else
q.push_back({nx, ny});
}
}
}
cout << ans << nl;
return 0;
}
