#include <bits/stdc++.h>
using namespace std;
#define task ""
#define fi first
#define se second
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORD(i, a, b) for (int i = (b), _a = (a); i >= _a; --i)
template <typename T1, typename T2> bool minimize(T1 &a, T2 b) {
if (a > b) {a = b; return true;} return false;
}
template <typename T1, typename T2> bool maximize(T1 &a, T2 b) {
if (a < b) {a = b; return true;} return false;
}
const int dx[] = {-1, 0, 0, +1};
const int dy[] = {0, -1, +1, 0};
const int MAX = 4000;
int n, m;
int ans = 0;
int d[MAX][MAX];
char a[MAX][MAX];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
if (fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
cin >> n >> m;
for (int i = 0; i < n; ++i)
for (int j = 0; j < m; ++j)
cin >> a[i][j];
memset(d, 0x3f, sizeof d);
deque<pair<int, int>> dq;
dq.push_front({0, 0});
d[0][0] = 1;
while (dq.size()) {
int u = dq.front().fi;
int v = dq.front().se;
maximize(ans, d[u][v]);
dq.pop_front();
for (int i = 0; i < 4; ++i) {
int x = u + dx[i], y = v + dy[i];
if (x < 0 || x >= n) continue;
if (y < 0 || y >= m) continue;
if (a[x][y] != '.') {
int w = a[u][v] != a[x][y];
if (minimize(d[x][y], d[u][v] + w)) {
if (w) dq.push_back({x, y});
else dq.push_front({x, y});
}
}
}
}
cout << ans;
return 0;
}
