#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MX = 4005;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
int H, W;
char grid[MX][MX];
int dist[MX][MX];
int main() {
cin.tie(0); ios_base::sync_with_stdio(0);
for(int i = 0; i < MX; i++)
for(int j = 0; j < MX; j++)
dist[i][j] = -1;
cin >> H >> W;
for(int i = 0; i < H; i++) {
for(int j = 0; j < W; j++) {
cin >> grid[i][j];
}
}
deque<pair<int,int>> dq;
dq.push_front({0, 0});
dist[0][0] = 0;
int ans = 0;
while(!dq.empty()) {
auto [x, y] = dq.front(); dq.pop_front();
ans = max(ans, dist[x][y]);
for(int k = 0; k < 4; k++) {
int nx = x + dx[k], ny = y + dy[k];
if(nx >= 0 && nx < H && ny >= 0 && ny < W && grid[nx][ny] != '.' && dist[nx][ny] == -1) {
if(grid[x][y] == grid[nx][ny]) {
dist[nx][ny] = dist[x][y];
dq.push_front({nx, ny});
} else {
dist[nx][ny] = dist[x][y] + 1;
dq.push_back({nx, ny});
}
}
}
}
cout << ans + 1 << '\n';
}
