// author: khba
#include "bits/stdc++.h"
using namespace std;
#ifdef khba
#include "C:\Users\Asus\Desktop\khba\debug.h"
#else
#define print(...) 42
#endif
int32_t main() {
#ifdef khba
freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);
#endif
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n, m;
cin >> n >> m;
vector<string> a(n);
for (string& s : a) cin >> s;
vector<vector<int>> dp(n, vector<int>(m, 1e9));
dp[0][0] = 1;
int ans = 0;
priority_queue<tuple<int, int, int>, vector<tuple<int, int, int>>, greater<>> q;
q.emplace(1, 0, 0);
while (q.size()) {
auto [d, u, v] = q.top();
q.pop();
if (dp[u][v] < d) continue;
ans = max(ans, dp[u][v]);
if (u > 0 and dp[u - 1][v] > dp[u][v] + (a[u - 1][v] != a[u][v]) and a[u - 1][v] != '.') {
dp[u - 1][v] = dp[u][v] + (a[u - 1][v] != a[u][v]);
q.emplace(dp[u - 1][v], u - 1, v);
}
if (u + 1 < n and dp[u + 1][v] > dp[u][v] + (a[u + 1][v] != a[u][v]) and a[u + 1][v] != '.') {
dp[u + 1][v] = dp[u][v] + (a[u + 1][v] != a[u][v]);
q.emplace(dp[u + 1][v], u + 1, v);
}
if (v > 0 and dp[u][v - 1] > dp[u][v] + (a[u][v - 1] != a[u][v]) and a[u][v - 1] != '.') {
dp[u][v - 1] = dp[u][v] + (a[u][v - 1] != a[u][v]);
q.emplace(dp[u][v - 1], u, v - 1);
}
if (v + 1 < m and dp[u][v + 1] > dp[u][v] + (a[u][v + 1] != a[u][v]) and a[u][v + 1] != '.') {
dp[u][v + 1] = dp[u][v] + (a[u][v + 1] != a[u][v]);
q.emplace(dp[u][v + 1], u, v + 1);
}
}
cout << ans;
return 0;
}
