// problem url: https://oj.uz/problem/view/BOI13_tracks
#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector< vector<int> > vii;
const int INF = 1e9+7;
int h, w;
vector<string> snow;
int dx[4] = {-1,1,0,0};
int dy[4] = {0,0,-1,1};
bool inside(int x, int y) {
if (x < 0 || x >= h || y < 0 || y >= w) return false;
if (snow[x][y] == '.') return false;
return true;
}
/*
inp:
5 8
FFR.....
.FRRR...
.FFFFF..
..RRRFFR
.....FFF
out:
2
*/
void solve() {
cin >> h >> w;
snow.resize(h);
for (int i = 0; i < h; i++) cin >> snow[i];
vii d(h, vi(w, 0));
// no rabbits or foxes
if (snow[0][0] == '.') { cout << 0 << '\n'; return; }
// initialize first cell
deque<pii> dq;
dq.push_back(pii(0,0));
d[0][0] = 1;
int ans = 1;
while (!dq.empty()) {
// auto [ux, uy] = dq.front() // for C++17
pii u = dq.front();
int ux = u.first, uy = u.second;
dq.pop_front();
ans = max(ans, d[ux][uy]);
for (int i = 0; i < 4; i++) {
int x = ux + dx[i], y = uy + dy[i];
// what if: d[ux][uy] + w < d[x][y]
// instead of d[x][y] == 0
// answer: just based on initialization
// it's better to use Dijkstra-style
if (!inside(x,y)) continue;
int w = snow[ux][uy] != snow[x][y];
if (d[x][y] == 0) {
d[x][y] = d[ux][uy] + w;
if (w) dq.push_back(pii(x,y));
else dq.push_front(pii(x,y));
}
}
}
cout << ans << '\n';
}
int main() {
ios::sync_with_stdio(false); cin.tie(nullptr);
int tt = 1;
// cin >> tt;
while (tt--) solve();
return 0;
}
