// IN THE NAME OF GOD
#include<bits/stdc++.h>
#define endl '\n'
#define file_reading freopen("input.txt", "r", stdin); freopen("output.txt", "w", stdout);
#define flush cout.flush();
using namespace std;
typedef long long ll;
typedef long double dll;
typedef unsigned long long ull;
const int N = 4e3+5, inf = 1e9;
int dat[N][N], dist[N][N], ans, must;
deque<pair<int,int>> q;
void dij(int n, int m){
for(int i=1; i<=n; i++) for(int j=1; j<=m; j++) dist[i][j] = inf;
dist[n][m] = 1;
q.push_front({n,m});
while(q.size()){
int x = q.front().first, y = q.front().second; q.pop_front();
ans = max(ans,dist[x][y]);
if (x-1 >= 1 && dat[x][y] == dat[x-1][y] && dist[x-1][y] >= inf) dist[x-1][y] = dist[x][y], q.push_front({x-1,y});
if (x+1 <= n && dat[x][y] == dat[x+1][y] && dist[x+1][y] >= inf) dist[x+1][y] = dist[x][y], q.push_front({x+1,y});
if (y-1 >= 1 && dat[x][y] == dat[x][y-1] && dist[x][y-1] >= inf) dist[x][y-1] = dist[x][y], q.push_front({x,y-1});
if (y+1 <= m && dat[x][y] == dat[x][y+1] && dist[x][y+1] >= inf) dist[x][y+1] = dist[x][y], q.push_front({x,y+1});
if (x-1 >= 1 && dat[x][y] != dat[x-1][y] && dat[x-1][y] && dist[x-1][y] >= inf) dist[x-1][y] = dist[x][y]+1, q.push_back({x-1,y});
if (x+1 <= n && dat[x][y] != dat[x+1][y] && dat[x+1][y] && dist[x+1][y] >= inf) dist[x+1][y] = dist[x][y]+1, q.push_back({x+1,y});
if (y-1 >= 1 && dat[x][y] != dat[x][y-1] && dat[x][y-1] && dist[x][y-1] >= inf) dist[x][y-1] = dist[x][y]+1, q.push_back({x,y-1});
if (y+1 <= m && dat[x][y] != dat[x][y+1] && dat[x][y+1] && dist[x][y+1] >= inf) dist[x][y+1] = dist[x][y]+1, q.push_back({x,y+1});
}
}
void solve(){
int n,m; cin >> n >> m;
for(int i=1; i<=n; i++){
for(int j=1; j<=m; j++){
char g; cin >> g;
if (g == '.') dat[i][j] = 0;
else if (g == 'R') dat[i][j] = 1, must++;
else dat[i][j] = 2, must++;
}
}
if (must == 0){cout << 0 << endl; return;}
dij(n,m);
cout << ans << endl;
}
int32_t main(){
ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
int t; t=1; //cin >> t;
while(t--){solve();}
}
