#include <bits/stdc++.h>
#define int int64_t
using namespace std;
void setIO() {
cin.tie(0)->sync_with_stdio(0);
}
bool inside(int x, int y, int n, int m, vector<string> &grid) {
return (x > -1 && x < n && y > -1 && y < m && grid[x][y] != '.');
}
void solve() {
//cout << "zco";
int n, m;
cin >> n >> m;
vector<string> grid(n);
for(auto &x : grid) cin >> x;
deque<pair<int, int>> dq;
dq.push_back({0, 0});
vector<vector<int>> depth(n, vector<int>(n, 1e18));
depth[0][0] = 0;
vector<int> di { -1, 0, 1, 0} , dj { 0, 1, 0, -1};
//auto inside = [](int x, int y, int &n, int &m) { return (x > -1 && x < n && y > -1 && y < m); };
int ans = 1;
while(!dq.empty()) {
auto u = dq.front();
dq.pop_front();
ans = max(ans, depth[u.first][u.second]);
for(int i = 0; i < 4; i++) {
int x = u.first+di[i], y = u.second+dj[i];
if(inside(x, y, n, m, grid) && (depth[x][y] + (grid[x][y] != grid[u.first][u.second])) < depth[x][y]) {
depth[x][y] = depth[u.first][u.second] + (grid[u.first][u.second] != grid[x][y]);
if(grid[u.first][u.second] != grid[x][y]) dq.push_back({x, y});
else dq.push_front({x, y});
}
}
}
cout << ans+1;
}
int32_t main() {
setIO();
solve();
return 0;
}
