#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pull;
typedef pair<int, int> pii;
typedef pair<ld, ld> pld;
int n, m;
int a[4009][4009];
int vis[4009][4009];
vector<pii> dir = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
queue<pii> q[2];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
//freopen("in.txt", "r", stdin);
//freopen("out.txt", "w", stdout);
cin >> n >> m;
for(int i = 0; i < n; ++i){
string s;
cin >> s;
for(int j = 0; j < m; ++j){
if(s[j] == 'F')
a[i][j] = 0;
else if(s[j] == 'R')
a[i][j] = 1;
else
a[i][j] = -1;
}
}
q[a[0][0]].push({0, 0});
int cur = a[0][0];
vis[0][0] = 1;
int ans = 0;
while(q[0].size() || q[1].size()){
++ans;
while(q[cur].size()){
pii x = q[cur].front();
q[cur].pop();
for(auto u : dir){
int x1 = x.ff + u.ff;
int y1 = x.ss + u.ss;
if(x1 < 0 || x1 >= n || y1 < 0 || y1 >= m)
continue;
if(a[x1][y1] != -1 && vis[x1][y1] == 0){
q[a[x1][y1]].push({x1, y1});
vis[x1][y1] = 1;
}
}
}
cur ^= 1;
}
cout << ans << '\n';
}
