#include "bits/stdc++.h"
using namespace std;

#define rep(i, a, b) for(int i=a; i<=b; i++)
#define trav(a, x) for(auto& a:x)
#define all(x) begin(x), end(x)
#define sz(x) (int) x.size()
#define f first
#define s second
#define nl "\n"
#define pb push_back
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
const int MOD=3;
template<class T> using pqg=priority_queue<T, vector<T>, greater<T>>;

int col[400000];
int cnt[400001];
int n;
string s;
map<char, int> mp;
map<int, char> rmp;
const int MAXN=500000;
ll fac[MAXN+5];

ll inv(ll a){
  if(a==1) return 1;
  if(a==2) return 2;
}

ll choose(ll n, ll k){
  if(k>n) return 0;
  if(cnt[n]>cnt[n-k]+cnt[k]) return 0;
  return (fac[n]*inv(fac[k])*inv(fac[n-k]))%3;
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  // freopen("input.txt", "r", stdin); 
  // freopen("output.txt", "w", stdout);

  cin >> n;
  fac[0]=1;
  for(ll i=1; i<=n; i++){
    int x=i;
    while(x/3){
      cnt[i]+=x/3;
      x/=3;
    }
    x=i;
    while(x%3==0) x/=3;
    fac[i]=(fac[i-1]*x)%3;
    // cout << i << " fac " << fac[i] << nl;
  }
  
  cin >> s;
  mp['R']=0;
  mp['B']=1;
  mp['W']=2;
  rmp[0]='R';
  rmp[1]='B';
  rmp[2]='W';
  int ans=0;
  rep(i, 0, n-1){
    // cout << mp[s[i]] << nl;
    // cout << choose(n-1, i) << " ";
    ans+=choose(n-1, i)*mp[s[i]];
    ans%=3;
  }
  if(n%2==0) ans=(3-ans)%3;
  cout << rmp[ans];
}
#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

// nCk mod p
struct Lucas {
    vector<vector<long long>> table;
    long long p; // prime number
    Lucas(long long _p) : p(_p) { init(p); }

    void init(long long p) {
        table.assign(p, vector<long long> (p));
        table[0][0] = 1;
        for(int i = 1; i < p; i++) {
            table[i][0] = 1;
            for(int j = i; j > 0; j--) {
                table[i][j] = (table[i - 1][j - 1] + table[i - 1][j]) % p;
            }
        }
    }

    long long comb(long long n, long long k) {
        long long ret = 1;
        while(n | k) {
            ret *= table[n % p][k % p];
            ret %= p;
            n /= p;
            k /= p;
        }
        return ret;
    }

};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);

    int n; string s; cin >> n >> s;
    int B = 0, W = 1, R = 2;
    vector<int> a(n);
    rep(i,n){
        if(s[i] == 'B') a[i] = B;
        if(s[i] == 'W') a[i] = W;
        if(s[i] == 'R') a[i] = R;
    }

    Lucas l(3);
    int ans = 0;
    rep(i,n) ans = (ans + l.comb(n - 1, i) * a[i]) % 3;
    if(n % 2 == 0) ans = (-ans + 3) % 3;
    if(ans == B) cout << 'B' << endl;
    if(ans == W) cout << 'W' << endl;
    if(ans == R) cout << 'R' << endl;
}