#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<pair<int, int>> vii;
typedef pair<int, int> pi;
#define MOD 1000000007LL
int H, W;
string grid[4000];
int depth[4000][4000];
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
bool ins(int x, int y) {
return x >= 0 && y >= 0 && x < H && y < W && grid[x][y] != '.';
}
int main() {
cin >> H >> W;
for (int i = 0; i < H; i++) cin >> grid[i];
for (int i = 0; i < H; i++)
for (int j = 0; j < W; j++) depth[i][j] = 1e9;
depth[0][0] = 1;
int ans = 1;
deque<pair<int, int>> q; q.push_front({0, 0});
while (!q.empty()) {
int vr = q.front().first, vc = q.front().second; q.pop_front();
ans = max(ans, depth[vr][vc]);
for (int i = 0; i < 4; i++) {
int nr = vr + dx[i], nc = vc + dy[i];
if (ins(nr, nc) == false) continue;
int w = grid[vr][vc] != grid[nr][nc];
if (depth[vr][vc]+w < depth[nr][nc]) {
depth[nr][nc] = depth[vr][vc]+w;
if (w == 0) q.push_front({nr, nc});
else q.push_back({nr, nc});
}
}
//cout << "Finished rep for " << vr << " " << vc << " " << depth[vr][vc] << endl;
}
cout << ans << endl;
/*cout << "Debugging depth" << endl;
for (int i = 0; i < H; i++) {
for (int j = 0; j < W; j++) {
cout << depth[i][j] << " ";
}
cout << endl;
}*/
}
