/*
This code belongs to Aadit Ambadkar
Date: 2022-03-07 21:34:47
Problem: tis
*/
#include <bits/stdc++.h>
using namespace::std;
typedef long long ll;
#define F0R(i, n) for (int i = 0; i < n; i++)
#define R0F(i, n) for (int i = n-1; i >= 0; i--)
#define FOR(i, a, n) for (int i = a; i < n; i++)
#define pb push_back
#define fastio ios::sync_with_stdio(0); cin.tie(0)
#define MOD 1000000007
#define FF first
#define SS second
int n, m;
int board[4005][4005];
bool vis[4005][4005];
int main() {
fastio;
cin >> n >> m;
F0R(i, n) {
string s;
cin >> s;
F0R(j, m) {
if (s[j]=='F') board[i][j]=1;
else if (s[j]=='R') board[i][j]=2;
else board[i][j]=0;
vis[i][j]=false;
}
}
// F0R(i, n) {
// F0R(j, m) {
// cout << board[i][j] << " ";
// }
// cout << "\n";
// }
// cout << "\n";
deque<pair<int, pair<int, int>>> pq;
pq.push_front({1, {0, 0}});
vis[0][0]=true;
int ans = 0;
while (!pq.empty()) {
auto p = pq.front(); pq.pop_front();
int g = p.FF, u = p.SS.FF, v = p.SS.SS;
// if (vis[u][v]) continue;
// cout << u << " " << v << " " << g << "\n";
ans = max(ans, g);
vis[u][v]=true;
if (u < n-1 && !vis[u+1][v] && board[u+1][v]!=0) {
vis[u+1][v]=true;
if (board[u][v]==board[u+1][v]) pq.push_front({g, {u+1, v}});
else pq.push_back({g+1, {u+1, v}});
}
if (v < m-1 && !vis[u][v+1] && board[u][v+1]!=0) {
vis[u][v+1]=true;
if (board[u][v]==board[u][v+1]) pq.push_front({g, {u, v+1}});
else pq.push_back({g+1, {u, v+1}});
}
if (u > 0 && !vis[u-1][v] && board[u-1][v]!=0) {
vis[u-1][v]=true;
if (board[u][v]==board[u-1][v]) pq.push_front({g, {u-1, v}});
else pq.push_back({g+1, {u-1, v}});
}
if (v > 0 && !vis[u][v-1] && board[u][v-1]!=0) {
vis[u][v-1]=true;
if (board[u][v]==board[u][v-1]) pq.push_front({g, {u, v-1}});
else pq.push_back({g+1, {u, v-1}});
}
}
cout << ans;
return 0;
}
