#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define mp make_pair
#define F first
#define S second
constexpr int maxn = 4000;
int h, w;
char grid[maxn][maxn];
int dist[maxn][maxn];
pii dir[4] = {mp(1, 0), mp(-1, 0), mp(0, 1), mp(0, -1)};
deque<pii> q;
pii vsum(pii a, pii b) { return mp(a.F + b.F, a.S + b.S); }
int main() {
// ios_base::sync_with_stdio(false);
// cin.tie(NULL);
cin >> h >> w;
for (int r = 0; r < h; r++) {
for (int c = 0; c < w; c++) {
cin >> grid[r][c];
dist[r][c] = maxn * maxn;
}
}
// for (auto p : dir) cout << p.F << ' ' << p.S << '\n';
dist[0][0] = 0;
q.push_front(mp(0, 0));
while (!q.empty()) {
pii cell = q.front();
q.pop_front();
for (int i = 0; i < 4; i++) {
pii nbr = vsum(cell, dir[i]);
if (nbr.F < 0 || nbr.F >= h || nbr.S < 0 || nbr.S >= w) continue;
if (grid[nbr.F][nbr.S] == '.') continue;
int wgt = (grid[cell.F][cell.S] == grid[nbr.F][nbr.S] ? 0 : 1);
// cout << "checked " << cell.F << cell.S << " " << nbr.F << nbr.S << '\t' << wgt << '\n';
if (dist[cell.F][cell.S] + wgt < dist[nbr.F][nbr.S]) {
dist[nbr.F][nbr.S] = dist[cell.F][cell.S] + wgt;
if (wgt == 1)
q.push_back(nbr);
else
q.push_front(nbr);
}
}
}
int ans = 0;
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
// cout << (dist[i][j] == maxn * maxn ? -1 : dist[i][j]) << '\t';
if (grid[i][j] != '.') ans = max(ans, dist[i][j]);
}
// cout << '\n';
}
cout << ans + 1 << '\n';
return 0;
}
