#include <bits/stdc++.h>
using namespace std;
int h, w, total;
int meadow[4005][4005];
bool vis[4005][4005];
// vector<pair<int, int>> dir = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
int dir[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
int main() {
cin >> h >> w;
char in;
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
cin >> in;
if (in == '.') {
meadow[i][j] = -1;
} else if (in == 'R') {
meadow[i][j] = 1;
total++;
}
else {
meadow[i][j] = 0;
total++;
}
}
}
// for (int i = 1; i <= h; i++) {
// for (int j = 1; j <= w; j++) {
// cout << meadow[i][j] << "\t";
// }
// cout << endl;
// }
int ans = 0;
while (true) {
queue<pair<int, int>> q;
memset(vis, 0, sizeof(vis));
q.push({1, 1});
vis[1][1] = 1;
int row, col, count = 1;
int top = meadow[1][1];
meadow[1][1] += 1;
meadow[1][1] %= 2;
ans++;
while (!q.empty()) {
row = q.front().first;
col = q.front().second;
q.pop();
for (int i = 0; i < 4; i++) {
if (row + dir[i][0] > 0 and row + dir[i][0] <= h and col + dir[i][1] > 0 and col + dir[i][1] <= w and !vis[row+dir[i][0]][col+dir[i][1]] and meadow[row+dir[i][0]][col+dir[i][1]] == top) {
q.push({row+dir[i][0], col+dir[i][1]});
meadow[row+dir[i][0]][col+dir[i][1]] += 1;
meadow[row+dir[i][0]][col+dir[i][1]] %= 2;
vis[row+dir[i][0]][col+dir[i][1]] = 1;
count++;
}
}
}
// for (int i = 1; i <= h; i++) {
// for (int j = 1; j <= w; j++) {
// cout << meadow[i][j] << "\t";
// }
// cout << endl;
// }
// cout << count << " " << total << endl;
// cout << endl;
// break;
if (count == total) {
cout << ans << endl;
return 0;
}
}
}
