#include <bits/stdc++.h>
using namespace std;
#define int int64_t
#define pii pair<int, int>
vector<pii> dir = {{0, 1}, {-1, 0}, {1, 0}, {0, -1}};
int n, m;
pii operator+(const pii &x, const pii &y) {
return {x.first + y.first, x.second + y.second};
}
bool check(const pii &x) {
return x.first >= 0 && x.first < n && x.second >= 0 && x.second < m;
}
signed main() {
cin>>n>>m;
vector<string> a(n);
for (auto &x:a)cin>>x;
vector<vector<int>> d(n, vector<int>(m, 1e9));
deque<pii> dq;
dq.push_front({0, 0});
d[0][0]=1;
int mx = 0;
while (!dq.empty()) {
pii t = dq.front();dq.pop_front();
mx = max(mx, d[t.first][t.second]);
// test all dir
for (pii x:dir) {
pii temp = t + x;
if (check(temp) && a[temp.first][temp.second] != '.') {
int w = (a[t.first][t.second] != a[temp.first][temp.second]);
if (d[t.first][t.second] + w < d[temp.first][temp.second]) {
if (w == 0) {
dq.push_front(temp);
}
else {
dq.push_back(temp);
}
d[temp.first][temp.second]=d[t.first][t.second]+w;
}
}
}
}
cout << mx << "\n";
}
