#include <bits/stdc++.h>
#include <deque>
using namespace std;
// dbg
#ifdef LOCAL
#include "../dbg.h"
#else
#define dbg(...)
#endif
// typedefs
using ll = long long;
#define LONG_LONGS
#ifdef LONG_LONGS
#define int ll
const int inf = (int)1e18;
#else
const int inf = int(1e9);
#endif
using vi = vector<int>;
using vvi = vector<vi>;
using p2 = pair<int, int>;
using vp2 = vector<p2>;
using vvp2 = vector<vp2>;
#define rep(i, high) for (int i = 0; i < high; i++)
#define repp(i, low, high) for (int i = low; i < high; i++)
#define repe(i, container) for (auto& i : container)
#define per(i, high) for (int i = high - 1; i >= 0; i--)
#define perr(i, high, low) for (int i = high - 1; i >= low; i--)
// Builtins
#define clz(x) __builtin_clz(x)
#define popcount(x) __builtin_popcountll(x)
// Fast I/O
inline void fast() {
ios::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
}
#define gc() getchar_unlocked()
inline void read(int& v) {
v = 0;
int sign = 1;
char c = gc();
if (c == '-') {
sign = -1;
} else {
v += c - '0';
}
while ((c = gc()) && c != ' ' && c != '\n') {
if (c == EOF) {
v = -1;
return;
}
v *= 10;
v += c - '0';
}
v *= sign;
}
inline void read(int& u, int& v) {
read(u);
read(v);
}
inline void read(int& u, int& v, int& k) {
read(u);
read(v);
read(k);
}
// inline void read(int& v) { char c; while ((c = getchar()) != EOF && c != ' '
// && c != '\n') { v *= 10; v += c - '0'; } }
inline void read(string& s) {
char c;
while ((c = gc()) != EOF && c != '\n' && c != ' ') {
s.push_back(c);
}
}
inline void readline(string& s) {
char c;
while ((c = gc()) != EOF && c != '\n') {
s.push_back(c);
}
}
void readinput() {} // Recursion base case
template <typename T, typename... Args>
void readinput(T& arg, Args&... args) {
read(arg);
readinput(args...);
}
#define dread(type, ...) \
type __VA_ARGS__; \
readinput(__VA_ARGS__);
template <typename T>
istream& operator>>(istream& is, vector<T>& v) {
repe(u, v) read(u);
return is;
}
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define setcontains(set, x) (set.find(x) != set.end())
#define sz(container) ((int)container.size())
vector<p2> dirs = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
// time and rng
auto Start = chrono::high_resolution_clock::now();
void resettimer() {
Start = chrono::high_resolution_clock::now();
}
int elapsedmillis() {
return chrono::duration_cast<chrono::milliseconds>(
chrono::high_resolution_clock::now() - Start
)
.count();
}
random_device rd;
mt19937 rng(rd());
template <typename T, typename U>
inline int randint(T lo, U hi) {
return uniform_int_distribution<int>((int)lo, (int)hi)(rng);
} // [lo,hi]
template <typename T>
inline T randel(vector<T>& v) {
return v[uniform_int_distribution<int>(int(0), int(v.size()) - int(1))(rng)];
} // [lo,hi]
#define bet(lo, i, hi) (((lo) <= (i)) && ((i) < (hi)))
const int H = 4000;
const int W = 4000;
int grid[H][W];
int h, w;
/*
* 0 -> '.'
* 1 -> 'F'
* 2 -> 'R'
*/
/*
int fcnt = 0;
int rcnt = 0;
bool vis[H][W];
void dfs(int r, int c, bool rec) {
if (!(bet(0, r, h) && bet(0, c, w))) return;
if (vis[r][c]) return;
dbg(r, c, rec);
vis[r][c] = 1;
if (!rec) {
if (grid[r][c] == 1) fcnt++;
if (grid[r][c] == 2) rcnt++;
}
repe(dir, dirs) {
int rr = r + dir.first;
int cc = c + dir.second;
if (!(bet(0, rr, h) && bet(0, cc, w))) continue;
if (grid[r][c] == grid[rr][cc]) dfs(rr, cc, true);
}
}
*/
// Depth of conected component tree
bool vis[H][W] = {0};
int bfs(int r, int c) {
int ans = 0;
vis[r][c] = 1;
deque<tuple<int, int, int>> dq;
dq.push_front({r, c, 0});
while (!dq.empty()) {
int rr, cc, vv;
tie(rr, cc, vv) = dq.front();
dq.pop_front();
ans = max(ans, vv);
vis[rr][cc] = 1;
repe(dir, dirs) {
int rrr = rr + dir.first;
int ccc = cc + dir.second;
if (!(bet(0, rrr, h) && bet(0, ccc, w)))
continue;
if (vis[rrr][ccc])
continue;
if (grid[rr][cc] == grid[rrr][ccc])
dq.push_front({rrr, ccc, vv});
else if (grid[rrr][ccc] > 0)
dq.push_back({rrr, ccc, vv + 1});
}
}
return ans + 1;
}
signed main() {
fast();
cin >> h >> w;
rep(i, h) {
string line;
cin >> line;
dbg(line);
rep(j, w) {
if (line[j] == '.') {
grid[i][j] = 0;
}
if (line[j] == 'F') {
grid[i][j] = 1;
}
if (line[j] == 'R') {
grid[i][j] = 2;
}
}
}
rep(i, h) {
dbg(grid[i]);
}
/*
rep(i, h) {
rep(j, w) {
dfs(i, j, false);
}
}
dbg(fcnt, rcnt);
cout << 1 + min(fcnt, rcnt);
*/
int ans = bfs(0, 0);
cout << ans;
return 0;
}
