import java.io.*;
import java.util.*;
public class tracks {
static final int[] dx = {0, 0, -1, 1};
static final int[] dy = {-1, 1, 0, 0};
static int N = 1, H, W;
static int[][] grid, count;
public static void main(String[] args) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
PrintWriter pw = new PrintWriter(System.out);
StringTokenizer st = new StringTokenizer(br.readLine());
H = Integer.parseInt(st.nextToken());
W = Integer.parseInt(st.nextToken());
grid = new int[H][W];
for (int i = 0; i < H; i++) {
String line = br.readLine();
for (int j = 0; j < W; j++) {
grid[i][j] = (line.charAt(j) == 'F') ? 1
: (line.charAt(j) == 'R') ? 2
: -1;
}
}
br.close();
pw.println(bfs());
pw.flush();
}
private static int bfs() {
count = new int[H][W];
LinkedList<int[]> q = new LinkedList<>();
q.add(new int[]{0, 0});
count[0][0] = 1;
while (!q.isEmpty()) {
int[] curr = q.poll();
N = Math.max(N, count[curr[0]][curr[1]]);
for (int i = 0; i < 4; i++) {
int nx = curr[0] + dx[i];
int ny = curr[1] + dy[i];
if (nx < 0 || ny < 0 || nx >= H || ny >= W) continue;
if (count[nx][ny] > 0) continue;
if (grid[nx][ny] == -1) continue;
if (grid[nx][ny] != grid[curr[0]][curr[1]]) {
count[nx][ny] = count[curr[0]][curr[1]] + 1;
q.addLast(new int[]{nx, ny});
} else {
count[nx][ny] = count[curr[0]][curr[1]];
q.addFirst(new int[]{nx, ny});
}
}
}
return N;
}
}
