#include <bits/stdc++.h>
//#define int long long
using namespace std;
const int MAX=4e3+5;
const int INF=1e18;
const int MOD=1e9+7;
const int MAXL=32;
int dx[]={-1,0,1,0},dy[]={0,1,0,-1};
int g[MAX][MAX][2],h,w; // {T,R,B,L} , vertex-info (4)
bool chk(int x,int y) {
return (x>=0 && y>=0 && x<h && y<w && g[x][y][0]!=-1);
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
//cout<<setprecision(6)<<fixed;
//freopen("input.txt","r",stdin);
//freopen("output.txt","w",stdout);
cin>>h>>w;
for(int i=0;i<h;i++) {
for(int j=0;j<w;j++) {
char s;
cin>>s;
if(s=='R') {
g[i][j][0]=0;
} else if(s=='F') {
g[i][j][0]=1;
} else {
g[i][j][0]=-1;
}
}
}
deque<tuple<int,int,int>>dq; //{x,y,dist}
dq.push_front({0,0,1});
int ans=1;
while(!dq.empty()) {
tuple<int,int,int>curr=dq.front();
dq.pop_front();
int x=get<0>(curr),y=get<1>(curr),d=get<2>(curr);
if(g[x][y][1]>0) {
continue;
}
g[x][y][1]=d;
ans=max(ans,d);
for(int i=0;i<4;i++) {
int nx=x+dx[i],ny=y+dy[i];
if(!chk(nx,ny) || g[nx][ny][1]>0) {
continue;
}
if(g[x][y][0]==g[nx][ny][0]) {
dq.push_front({nx,ny,d});
} else {
dq.push_back({nx,ny,d+1});
}
}
}
cout<<ans;
return 0;
}
