#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
const pii dd[4] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
int n, m, grid[4000][4000], dist[4000][4000], ans;
deque<pii> q;
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
memset(dist, 0x3f, sizeof dist);
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') grid[i][j] = 1; else if (s[j] == 'R') grid[i][j] = 2;
}
q.push_front({0, 0});
dist[0][0] = 0;
while (!q.empty()) {
auto [x, y] = q.front(); q.pop_front();
for (auto [dx, dy]: dd) {
auto xx = x + dx, yy = y + dy;
if (xx < 0 || yy < 0 || xx >= n || yy >= m || !grid[xx][yy]) continue;
if (grid[x][y] == grid[xx][yy]) {
if (dist[x][y] < dist[xx][yy]) {
dist[xx][yy] = dist[x][y];
q.push_front({xx, yy});
}
} else {
if (dist[x][y] + 1 < dist[xx][yy]) {
dist[xx][yy] = dist[x][y] + 1;
q.push_back({xx, yy});
}
}
}
}
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) if (grid[i][j]) ans = max(ans, dist[i][j]);
cout << ans+1;
}
