// https://oj.uz/problem/view/BOI13_tracks
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
using namespace std;
#define pii pair<int, int>
#define mp make_pair
#define maxHW 4000
bool seen[maxHW][maxHW];
string grid[maxHW];
char invert(char c) {
return (c == 'R') ? 'F' : 'R';
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int h, w;
cin >> h >> w;
int tracks = 0;
for (int i = 0; i < h; i++) {
cin >> grid[i];
for (int j = 0; j < w; j++) {
tracks += (grid[i][j] != '.');
}
}
set<pii> waiting({mp(0, 0)});
char waiting_color = grid[0][0];
int ans = 0;
int num_seen = 0;
while (num_seen < tracks) {
ans++;
queue<pii> Q;
for (auto [r, c] : waiting) {
Q.push(mp(r, c));
}
waiting.clear();
while (!Q.empty()) {
auto [r, c] = Q.front(); Q.pop();
num_seen += !seen[r][c];
seen[r][c] = true;
for (auto [nr, nc] : {mp(r + 1, c), mp(r - 1, c), mp(r, c + 1), mp(r, c - 1)}) {
if (0 <= nr && nr < h && 0 <= nc && nc < w && !seen[nr][nc]) {
if (grid[nr][nc] == waiting_color) {
Q.push(mp(nr, nc));
}
else if (grid[nr][nc] == invert(waiting_color)) {
waiting.insert(mp(nr, nc));
}
}
}
}
waiting_color = invert(waiting_color);
}
cout << ans << '\n';
}
