#include <bits/stdc++.h>
using namespace std;
vector<int> dx{-1, 1, 0, 0}, dy{0, 0, -1, 1};
int main() {
int h, w;
cin >> h >> w;
vector<vector<int>> field(h, vector<int>(w, 0)), rank(h, vector<int>(w, -1));
for (int i = 0; i < h; ++i) {
string line;
cin >> line;
for (int j = 0; j < w; ++j) field[i][j] = (line[j] == '.' ? -1 : (line[j] == 'R' ? 1 : 2));
}
int m = 1;
rank[0][0] = 1;
deque<vector<int>> q;
vector<int> first{0, 0};
q.push_back(first);
while (!q.empty()) {
vector<int> s = q.front();
m = max(m, rank[s[0]][s[1]]);
q.pop_front();
for (int i = 0; i < 4; ++i) {
int x = s[0] + dx[i], y = s[1] + dy[i];
if (x < 0 || y < 0 || x >= h || y >= w) continue;
if (rank[x][y] > 0 || field[x][y] < 0) continue;
vector<int> add{x, y};
if (field[s[0]][s[1]] == field[x][y]) q.push_front(add);
else q.push_back(add);
rank[x][y] = rank[s[0]][s[1]] + (field[s[0]][s[1]] == field[x][y] ? 0 : 1);
}
}
cout << m;
return 0;
}
