#include <iostream>
#include <vector>
#include <deque>
#define MAXN 4005
#define MAXV 17000000
int n, m;
std::vector<std::pair<int, bool> > Adj[MAXV];
int mat[MAXN][MAXN];
int main()
{
std::ios::sync_with_stdio(false);
std::cin >> n >> m;
for(int i = 0; i < n; i++)
{
for(int j = 0; j < m; j++)
{
char c;
std::cin >> c;
if(c == 'R')
mat[i][j] = 1;
else if(c == 'F')
mat[i][j] = 2;
else
mat[i][j] = 0;
}
}
for(int i = 0; i < n; i++)
{
for(int j = 0; j < m; j++)
{
int u = i*m + j;
if(mat[i][j])
{
if(i && mat[i-1][j])
{
bool type = (mat[i-1][j] != mat[i][j]);
int v = (i-1)*m + j;
Adj[u].push_back({v, type});
Adj[v].push_back({u, type});
}
if(j && mat[i][j-1])
{
bool type = (mat[i][j-1] != mat[i][j]);
int v = i*m + j - 1;
Adj[u].push_back({v, type});
Adj[v].push_back({u, type});
}
}
}
}
std::deque<int> bfs;
int d[MAXV];
bool vis[MAXV];
d[0] = 0;
for(int i = 0; i < MAXV; i++)
vis[i] = false;;
bfs.push_front(0);
vis[0] = true;
int answer = 0;
while(!bfs.empty())
{
int u = bfs.front();
bfs.pop_front();
for(std::pair<int, bool> v : Adj[u])
{
if(!vis[v.first])
{
vis[v.first] = true;
d[v.first] = d[u];
if(v.second)
{
bfs.push_back(v.first);
d[v.first]++;
}
else
bfs.push_front(v.first);
answer = std::max(answer, d[v.first]);
}
}
}
std::cout << answer+1 << std::endl;
return 0;
}
