#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second
#define pb push_back
#define rep(i,a,b) for (int i = a; i <= b; ++i)
#define all(v) (v).begin(), (v).end()
const int MAXN = 4e3 + 10;
const int INF = 1e18;
const int MOD = 1e9 + 7;
int a[MAXN][MAXN], dist[MAXN][MAXN], seen[MAXN][MAXN];
int dx[] = {0,1,0,-1};
int dy[] = {1,0,-1,0};
void solve() {
int n,m;
cin >> n >> m;
rep(i,1,n) {
rep(j,1,m) {
char ch;cin >> ch;
a[i][j] = (ch == 'F' ? 1LL : ch == 'R' ? 2 : 0);
}
}
deque<pii> q;
q.push_back({1,1});
seen[1][1] = 1;
dist[1][1] = 1;
int mx = 1;
while (!q.empty()) {
auto [x,y] = q.front();q.pop_front();
rep(k,0,3) {
int nx = x + dx[k], ny = y + dy[k];
if (nx < 1 || ny < 1 || nx > n || ny > m || seen[nx][ny] || a[nx][ny] == 0) continue;
seen[nx][ny] = 1;
dist[nx][ny] = dist[x][y] + (a[x][y] != a[nx][ny]);
mx = max(mx,dist[nx][ny]);
//cout << nx << ' ' << ny << ' ' << dist[nx][ny] << ' ' << (a[x][y] == a[nx][ny]) << '\n';
if (a[x][y] == a[nx][ny]) q.push_front({nx,ny});
else q.push_back({nx,ny});
}
}
cout << mx << '\n';
}
int32_t main() {
ios_base::sync_with_stdio(false);cin.tie(0);
int tt = 1;
//cin >> tt;
while (tt-- > 0) solve();
}
