#include <bits/stdc++.h>
using namespace std;
void solve()
{
int h, w;
cin >> h >> w;
vector<vector<int>> grid(h, vector<int>(w));
for (int i = 0; i < h; i++)
{
for (int j = 0; j < w; j++)
{
char c;
cin >> c;
if (c == '.')
grid[i][j] = 0;
else if (c == 'R')
grid[i][j] = 1;
else if (c == 'F')
grid[i][j] = 2;
}
}
int n = 0;
vector<vector<int>> d(h, vector<int>(w, 0));
deque<pair<int, int>> dq;
for (dq.emplace_front(0, 0), d[0][0] = 1; !dq.empty();)
{
auto [y, x] = dq.front();
dq.pop_front();
n = max(n, d[y][x]);
for (auto [dx, dy] : {pair(0, -1), pair(0, 1), pair(-1, 0), pair(1, 0)})
{
if (x + dx >= 0 && x + dx < w && y + dy >= 0 && y + dy < h)
{
if (grid[y + dy][x + dx] && d[y + dy][x + dx] == 0)
{
if (grid[y + dy][x + dx] == grid[y][x])
{
d[y + dy][x + dx] = d[y][x];
dq.emplace_front(y + dy, x + dx);
}
else
{
d[y + dy][x + dx] = d[y][x] + 1;
dq.emplace_back(y + dy, x + dx);
}
}
}
}
}
cout << n << '\n';
}
int main()
{
ios_base::sync_with_stdio(false), cin.tie(NULL);
solve();
return 0;
}
