#include <bits/stdc++.h>
using namespace std;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, 1, 0, -1};
const int MAXN = 4000 + 5;
int g[MAXN][MAXN];
int n, m;
int hsh(int i, int j)
{
return (i * m) + j;
}
int main()
{
cin >> n >> m;
bool visited[n][m];
for (int i = 0; i < n; i++)
{
for (int j = 0; j < m; j++)
{
char ch;
cin >> ch;
if (ch == '.')
g[i][j] = 0;
if (ch == 'R')
g[i][j] = 1;
if (ch == 'F')
g[i][j] = 2;
visited[i][j] = false;
}
}
vector<int> dx = {0, 1, 0, -1};
vector<int> dy = {1, 0, -1, 0};
int mxn = hsh(n - 1, m - 1);
vector<int> dd(mxn + 1, 1e9);
deque<pair<int, int>> q;
q.push_front({0, 0});
dd[0] = 1;
int ans = 0;
while (!q.empty())
{
pair<int, int> v = q.front();
int vhsh = hsh(v.first, v.second);
q.pop_front();
ans = max(ans, dd[vhsh]);
if (visited[v.first][v.second])
continue;
visited[v.first][v.second] = true;
int r = v.first;
int c = v.second;
for (int k = 0; k < 4; k++)
{
int rr = r + dx[k];
int cc = c + dy[k];
if (rr < 0 || rr >= n || cc < 0 || cc >= m)
continue;
if (visited[rr][cc])
continue;
if (g[rr][cc] == 0)
continue;
int khsh = hsh(rr, cc);
if (dd[vhsh] + (g[r][c] != g[rr][cc]) < dd[khsh])
{
dd[khsh] = dd[vhsh] + (g[r][c] != g[rr][cc]);
if (g[rr][cc] != g[r][c])
q.push_back({rr, cc});
else
q.push_front({rr, cc});
}
}
}
return cout << ans, 0;
//Olampiad ye tale bood
}
