#include <bits/stdc++.h>
#define Loop(x,l,r) for (ll x = (l); x < (r); ++x)
#define LoopR(x,l,r) for (ll x = (r)-1; x >= (l); --x)
typedef long long ll;
typedef std::pair<int, int> pii;
typedef std::pair<ll , ll > pll;
using namespace std;
const int N = 4010;
char s[N][N];
int dis[N][N];
int h, w;
bool in(int x, int y) {return 0 <= x && x < h && 0 <= y && y < w && s[x][y] != '.';}
void bfs()
{
Loop (i,0,N) Loop (j,0,N)
dis[i][j] = 1e9+10;
dis[0][0] = 0;
deque<pair<pii,int>> q;
q.push_back({{0,0},0});
while (q.size()) {
auto [dard, d] = q.front();
auto [i, j] = dard;
q.pop_front();
if (d != dis[i][j])
continue;
for (auto [x, y] : {pii{0, 1}, {0, -1}, {1, 0}, {-1, 0}}) {
x += i; y += j;
if (!in(x, y))
continue;
int w = s[i][j] != s[x][y];
if (dis[x][y] <= d + w)
continue;
dis[x][y] = d + w;
if (w == 0)
q.push_front({{x, y}, d + w});
else
q.push_back( {{x, y}, d + w});
}
}
}
int main()
{
cin.tie(0) -> sync_with_stdio(false);
cin >> h >> w;
Loop (i,0,h)
cin >> s[i];
bfs();
int ans = 0;
Loop (i,0,h) Loop (j,0,w)
if (in(i, j))
ans = max(ans, dis[i][j]);
cout << ans+1 << '\n';
}
