#include <iostream>
#include <vector>
#include <queue>
#include <utility>
using namespace std;
const int dx[4] = {0, 1, 0, -1};
const int dy[4] = {1, 0, -1, 0};
int main() {
int h, w;
cin >> h >> w;
vector<vector<int>> v(h, vector<int>(w, -1));
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
char c;
cin >> c;
switch (c) {
case 'F':
v[i][j] = 1;
break;
case 'R':
v[i][j] = 0;
break;
default:
v[i][j] = -1;
break;
}
}
}
deque<pair<int, int>> dq;
vector<vector<int>> dist(h, vector<int>(w));
dist[0][0] = 1;
dq.push_back({0, 0});
int ans = 0;
while (!dq.empty()) {
int x = dq.front().first;
int y = dq.front().second;
dq.pop_front();
ans = max(ans, dist[x][y]);
for (int i = 0; i < 4; i++) {
int nx = x + dx[i], ny = y + dy[i];
if (nx < 0 || nx >= h || ny < 0 || ny >= w || dist[nx][ny] || v[nx][ny] == -1) continue;
if (v[x][y] == v[nx][ny]) {
dist[nx][ny] = dist[x][y];
dq.push_front({nx, ny});
} else {
dist[nx][ny] = dist[x][y] + 1;
dq.push_back({nx, ny});
}
}
}
cout << ans << '\n';
/*
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
cout << dist[i][j] << ' ';
}
cout << endl;
}
*/
}
