#include <bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
int32_t main() {
int n, m;
cin >> n >> m;
char grid[n][m];
vector<vector<int>> distances(n, vector<int>(m, INT32_MAX));
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
cin >> grid[i][j];
vector<pair<int, int>> dirs = {{0,1}, {0,-1}, {1,0}, {-1,0}};
distances[0][0] = 0;
deque<pair<int, int>> que;
que.push_front({0, 0});
while (!que.empty()) {
auto curr = que.front(); que.pop_front();
for (auto& d : dirs) {
int nx = curr.fi + d.fi;
int ny = curr.se + d.se;
if (nx >= 0 && nx < n && ny >= 0 && ny < m && grid[nx][ny]!='.') {
int w = (grid[curr.fi][curr.se] == grid[nx][ny]) ? 0 : 1;
if (distances[curr.fi][curr.se] + w < distances[nx][ny]) {
distances[nx][ny] = distances[curr.fi][curr.se] + w;
if (w == 1) que.push_back({nx, ny});
else que.push_front({nx, ny});
}
}
}
}
int max_d = 0;
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
if(grid[i][j]!='.') max_d = max(max_d, distances[i][j]);
cout << max_d + 1 << '\n';
return 0;
}
