#include "bits/stdc++.h"
using namespace std;
#ifdef duc_debug
#include "bits/debug.h"
#else
#define debug(...)
#endif
const int movex[] = {1, -1, 0, 0};
const int movey[] = {0, 0, 1, -1};
const int maxn = 4005;
int n, m;
char a[maxn][maxn];
int d[maxn][maxn];
void solve() {
cin >> n >> m;
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= m; ++j) {
cin >> a[i][j];
}
}
deque<tuple<int, int, int>> dq;
dq.emplace_back(1, 1, 1);
memset(d, 0x3f, sizeof(d));
d[1][1] = 1;
while (!dq.empty()) {
auto [dist, x, y] = dq.front();
dq.pop_front();
if (dist > d[x][y]) continue;
for (int move = 0; move < 4; ++move) {
int r = x + movex[move], c = y + movey[move];
if (r < 1 || c < 1 || r > n || c > m || a[r][c] == '.') continue;
if (d[r][c] > d[x][y] + (a[r][c] != a[x][y])) {
d[r][c] = d[x][y] + (a[r][c] != a[x][y]);
if (a[r][c] == a[x][y]) {
dq.emplace_front(d[r][c], r, c);
} else {
dq.emplace_back(d[r][c], r, c);
}
}
}
}
int res = 0;
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= m; ++j) {
if (d[i][j] < 5e8) {
res = max(res, d[i][j]);
}
}
}
cout << res;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
solve();
return 0;
}
