//https://oj.uz/problem/view/BOI13_tracks
// __builtin_popcount(x) broj bitova
// __builtin_popcountll(x) long long
#define here cerr<<"---------------------------\n"
#include "bits/stdc++.h"
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#define ld double
#define ll long long
#define ull unsigned long long
#define llinf 100000000000000000LL // 10^17
#define iinf 2000000000 // 2*10^9
#define pb push_back
#define popb pop_back
#define fi first
#define sc second
#define endl '\n'
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pld pair<ld,ld>
#define sz(a) int(a.size())
#define all(a) a.begin(),a.end()
#define rall(a) a.begin(),a.end(),greater<int>()
#define getunique(v) {sort(all(v)); v.erase(unique(all(v)), v.end());}
using namespace std;
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
void setIO(string inoutname)
{
freopen((inoutname+".in").c_str(),"r",stdin);
freopen((inoutname+".out").c_str(),"w",stdout);
}
#define mod 1
ll gcd(ll a, ll b)
{
if(b==0) return a;
if(a==0) return b;
if(a>=b) return gcd(a%b,b);
return gcd(a,b%a);
}
ll lcm(ll a,ll b){
return (a/gcd(a,b))*b;
}
ll add(ll a,ll b){
a+=b;
a+=mod;
if(a>=mod) a%=mod;
return a;
}
ll mul(ll a,ll b){return(a*b)%mod;}
#define maxn 4005
ll a[maxn][maxn];
ll d[maxn][maxn];
ll n,m;
ll conv(char c){
if(c=='.') return 0;
if(c=='R') return 1;
return 2;
}
bool valid(ll x,ll y){
return (x>=1&&x<=n&&y>=1&&y<=m);
}
vector<ll> dx = {0,0,1,-1};
vector<ll> dy = {1,-1,0,0};
void tc(){
ios_base::sync_with_stdio(false);cerr.tie(0);cout.tie(0);cin.tie(0);
cin >> n >> m;
for(ll i = 1;i<=n;i++){
string s; cin >> s;
for(ll j = 1;j<=m;j++) a[i][j] = conv(s[j-1]);
}
deque<pll> q;
d[1][1] = 1;
q.pb({1,1});
ll ans = 0;
while(!q.empty()){
pll p = q.front();
q.pop_front();
ll x = p.fi,y = p.sc;
ans = max(ans,d[x][y]);
for(ll i = 0;i<4;i++){
ll x1 = x+dx[i];
ll y1 = y+dy[i];
if(valid(x1,y1)==0||d[x1][y1]) continue;
if(a[x1][y1]==0) continue;
if(a[x][y]==a[x1][y1]){
q.push_front({x1,y1});
d[x1][y1] = d[x][y];
}else{
q.pb({x1,y1});
d[x1][y1] = d[x][y]+1;
}
}
}
cout<<ans<<endl;
}
int main(){
ios_base::sync_with_stdio(false);cerr.tie(0);cout.tie(0);cin.tie(0);
//setIO("lol");
int t; t = 1;
while(t--){
tc();
}
return 0;
}
