import java.util.*;
import java.io.*;
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) {
FastIO io = new FastIO();
H = io.nextInt();
W = io.nextInt();
grid = new int[H][W];
for (int i = 0; i < H; i++) {
String line = io.next();
for (int j = 0; j < W; j++) {
grid[i][j] = (line.charAt(j) == 'F')?1:(line.charAt(j) == 'R')?2:-1;
}
}
io.println(bfs());
io.close();
}
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;
}
private static class FastIO extends PrintWriter {
private InputStream stream;
private byte[] buf = new byte[1<<16];
private int curChar, numChars;
// standard input
public FastIO() { this(System.in,System.out); }
public FastIO(InputStream i, OutputStream o) {
super(o);
stream = i;
}
// file input
public FastIO(String i, String o) throws IOException {
super(new FileWriter(o));
stream = new FileInputStream(i);
}
// throws InputMismatchException() if previously detected end of file
private int nextByte() {
if (numChars == -1) throw new InputMismatchException();
if (curChar >= numChars) {
curChar = 0;
try {
numChars = stream.read(buf);
} catch (IOException e) {
throw new InputMismatchException();
}
if (numChars == -1) return -1; // end of file
}
return buf[curChar++];
}
// to read in entire lines, replace c <= ' '
// with a function that checks whether c is a line break
public String next() {
int c; do { c = nextByte(); } while (c <= ' ');
StringBuilder res = new StringBuilder();
do { res.appendCodePoint(c); c = nextByte(); } while (c > ' ');
return res.toString();
}
public int nextInt() { // nextLong() would be implemented similarly
int c; do { c = nextByte(); } while (c <= ' ');
int sgn = 1; if (c == '-') { sgn = -1; c = nextByte(); }
int res = 0;
do {
if (c < '0' || c > '9')
throw new InputMismatchException();
res = 10*res+c-'0';
c = nextByte();
} while (c > ' ');
return res * sgn;
}
public double nextDouble() { return Double.parseDouble(next()); }
}
}
