#include<bits/stdc++.h>
using namespace std;
const int maxn = 4000 + 10, INF = 1e9 + 10;
int n, m, h, w, d[maxn][maxn], mx;
bool vis[maxn];
char meadow[maxn][maxn];
int main() {
memset(d, INF, sizeof(d));
cin >> h >> w;
for (int i = 1; i <= h; i++)
for (int j = 1; j <= w; j++)
cin >> meadow[i][j];
int adjx[4]{1, -1, 0, 0}, adjy[4]{0, 0, 1, -1};
d[1][1] = 0;
deque<pair<int, int>> q;
q.push_back({1, 1});
while (q.size()) {
auto v = q.front();
q.pop_front();
for (int i = 0; i < 4; i++) {
int x = v.first + adjx[i],
y = v.second + adjy[i];
if (x < 1 || y < 1 || x > h || y > w || meadow[x][y] == '.') continue;
int w = !(meadow[v.first][v.second] == meadow[x][y]);
if (d[v.first][v.second] + w < d[x][y]) {
d[x][y] = d[v.first][v.second] + w;
mx = max(mx, d[x][y]);
if (w == 1)
q.push_back({x, y});
else
q.push_front({x, y});
}
}
}
cout << mx + 1 << '\n';
return 0;
}
