#include <iostream>
#include <utility>
#include <deque>
#include <tuple>
using namespace std;
const int MAXN = 4005;
int n, m;
char table[MAXN][MAXN];
int levels[MAXN][MAXN];
pair<int, int> dirs[4] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> table[i][j];
}
}
deque<pair<int, int>> q; q.push_back({1, 1});
levels[1][1] = 1;
int ans = 1;
while (!q.empty()) {
int x, y; tie(x, y) = q.front();
q.pop_front();
ans = max(ans, levels[x][y]);
for (int d = 0; d < 4; d++) {
int x2 = x + dirs[d].first;
int y2 = y + dirs[d].second;
if (x2 < 1 || x2 > n || y2 < 1 || y2 > m) continue;
if (levels[x2][y2] != 0) continue;
if (table[x2][y2] == '.') continue;
if (table[x2][y2] == table[x][y]) {
q.push_front({x2, y2});
levels[x2][y2] = levels[x][y];
} else {
q.push_back({x2, y2});
levels[x2][y2] = 1 + levels[x][y];
}
}
}
cout << ans << endl;
return 0;
}
