#include <iostream>
#include <deque>
#include <vector>
using namespace std;
int dx[4]{0, 1, 0, -1};
int dy[4]{1, 0, -1, 0};
int main() {
int H, W;
cin >> H;
cin >> W;
vector<vector<int>> values(W, vector<int>(H, 0));
deque<pair<int,int>> q;
q.emplace_back(0, 0);
values[0][0] = 1;
vector<vector<int>> grid(W, vector<int>(H, -1));
for (int i = 0; i<H; i++) {
string line;
cin >> line;
for (int j = 0; j<W; j++) {
if (line.at(j) == 'F') {
grid[j][i] = 1;
} else if (line.at(j) == 'R') {
grid[j][i] = 0;
}
}
}
int solution = 1;
while (!q.empty()) {
const pair<int, int> el = q.front();
q.pop_front();
solution = max(solution, values[el.first][el.second]);
for (int i = 0; i<4; i++) {
const int x = el.first + dx[i];
const int y = el.second + dy[i];
if (x >= 0 && x<W && y>= 0 && y<H && values[x][y] == 0 && grid[x][y] != -1) {
if (grid[el.first][el.second] == grid[x][y]) {
q.emplace_front(x, y);
values[x][y] = values[el.first][el.second];
} else {
q.emplace_back(x, y);
values[x][y] = values[el.first][el.second] + 1;
}
}
}
}
cout << solution;
return 0;
}
