#include <bits/stdc++.h>
using namespace std;
#define LL long long
#define pb push_back
#define MOD 1000000007
#define vi vector<int>
#define pi pair<int, int>
char g[4005][4005];
int dist[4005][4005];
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};
int h, w, ans = 1;
int main()
{
//freopen("13_tracks.in", "r", stdin);
//freopen("13_tracks.out", "w", stdout);
ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin >> h >> w;
for (int i = 1; i <= h; ++i)
for (int j = 1; j <= w; ++j)
cin >> g[i][j];
deque<pi> q;
q.push_front({1, 1});
memset(dist, 0x3f, sizeof(dist));
//cout << dist[1][2] << endl;
dist[1][1] = 1;
while (!q.empty())
{
pi t = q.front(); q.pop_front();
int tx = t.first, ty = t.second;
ans = max(ans, dist[tx][ty]);
for (int i = 0; i < 4; ++i)
{
int x = tx + dx[i], y = ty + dy[i];
if (x < 1 || x > h || y < 1 || y > w || g[x][y] == '.') continue;
if (dist[x][y] > dist[tx][ty] + (g[x][y] != g[tx][ty]))
{
dist[x][y] = dist[tx][ty] + (g[x][y] != g[tx][ty]);
if (g[x][y] == g[tx][ty])
q.push_front({x, y});
else q.push_back({x, y});
}
}
}
/*
for (int i = 1; i <= h; ++i)
{
for (int j = 1; j <= w; ++j)
cout << dist[i][j] << " ";
cout << endl;
}
*/
cout << ans << endl;
return 0;
}
