#include <bits/stdc++.h>
using namespace std;
#define int long long
int dy[4] = {-1, 0, 1, 0};
int dx[4] = {0, 1, 0, -1};
void solve()
{
int H, W;
cin >> H >> W;
vector grid(H + 1, vector(W + 1, '.'));
for (int i = 1; i <= H; i++)
{
for (int j = 1; j <= W; j++)
{
cin >> grid[i][j];
}
}
priority_queue<pair<int,pair<int,int>>, vector<pair<int,pair<int,int>>>, greater<pair<int,pair<int,int>>>> pq;
vector dist(H + 1, vector(W + 1, (int)1E9));
vector vis(H + 1, vector(W + 1, false));
int ans = 1;
dist[1][1] = 1;
pq.push({1, {1,1}});
while (!pq.empty())
{
auto [a, b] = pq.top(); pq.pop();
auto [y, x] = b;
if (vis[y][x]) continue;
vis[y][x] = true;
ans = max(ans, a);
for (int k = 0; k < 4; k++)
{
int ny = y + dy[k], nx = x + dx[k];
if (ny < 1 || ny > H || nx < 1 || nx > W || grid[ny][nx] == '.') continue;
if (dist[y][x] + (grid[y][x] != grid[ny][nx]) < dist[ny][nx])
{
dist[ny][nx] = dist[y][x] + (grid[y][x] != grid[ny][nx]);
pq.push({dist[ny][nx], {ny, nx}});
}
}
}
cout << ans << '\n';
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(nullptr);
int tc = 1;
// cin >> tc;
while (tc--) solve();
return 0;
}
