#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 4e3 + 5;
int n, m, d[N][N], rab = 0, fox = 0;
char grid[N][N];
vector<int> dx = {-1, 0, 1, 0}, dy = {0, 1, 0, -1};
deque<pair<int, pair<int, int>>> dq;
bool inbound(int x, int y) {
return x >= 1 && x <= n && y >= 1 && y <= m && grid[x][y] != '.';
}
void bfs() {
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
d[i][j] = 1e18;
}
}
dq.push_front({1, {1, 1}});
d[1][1] = 1;
while (dq.size()) {
int p = dq.front().first, x = dq.front().second.first, y = dq.front().second.second; dq.pop_front();
if (p != d[x][y]) continue;
for (int k = 0; k < 4; k++) {
int tox = x + dx[k], toy = y + dy[k];
if (!inbound(tox, toy)) continue;
int c = grid[x][y] != grid[tox][toy];
if (d[tox][toy] <= d[x][y] + c) continue;
d[tox][toy] = d[x][y] + c;
if (c) dq.push_back({d[tox][toy], {tox, toy}});
else dq.push_front({d[tox][toy], {tox, toy}});
}
}
int ans = 0;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (d[i][j] != 1e18) ans = max(ans, d[i][j]);
}
}
cout << ans << '\n';
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
cin >> grid[i][j];
if (grid[i][j] == 'R') rab = 1;
if (grid[i][j] == 'F') fox = 1;
}
}
bfs();
return 0;
}
