// 2021-04-19 00:32:20
// clang-format off
#include <bits/stdc++.h>
#ifdef LOCAL
#include "lib/debug.hpp"
#else
#define debug(...) 1
#endif
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define rep(i, n) REP(i, 0, (n))
#define repc(i, n) REPC(i, 0, (n))
#define REP(i, n, m) for (int i = (int)(n); i < (int)(m); i++)
#define REPC(i, n, m) for (int i = (int)(n); i <= (int)(m); i++)
#define REPCM(i, n, m) for (int i = (int)(n); i >= (int)(m); i--)
template<class T> inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } else return false; }
template<class T> inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<int, int>;

// clang-format on
const int MX = 400040;
int n, c2[MX], c3[MX], x2, x3, y2, y3, z2, z3;
string s;
void answer() {
  cin >> n >> s;
  REPC(i, 1, n) {
    int j = i;
    while (j % 3 == 0) {
      c3[i]++;
      j /= 3;
    }
    if (j % 3 == 2) c2[i]++;
  }
  rep(i, n) {
    x2 += c2[i];
    x3 += c3[i];
    y2 += c2[i];
    y3 += c3[i];
  }
  int ans = 0;
  rep(i, n) {
    if (x3 == y3 + z3) {
      int color = 0;
      if (s[i] == 'B') color = 0;
      if (s[i] == 'W') color = 1;
      if (s[i] == 'R') color = 2;
      if ((x2 + y2 + z2) % 2) {
        ans += color * 2;
      } else {
        ans += color * 1;
      }
      ans %= 3;
    }
    y2 -= c2[n - i - 1];
    y3 -= c3[n - i - 1];
    z2 += c2[i + 1];
    z3 += c3[i + 1];
  }
  rep(i, n - 1) { (ans *= 2) %= 3; }
  if (ans == 0) cout << 'B' << '\n';
  if (ans == 1) cout << 'W' << '\n';
  if (ans == 2) cout << 'R' << '\n';
}

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);
  answer();
  return 0;
}
#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=4e5+1000;
typedef long long LL;
const LL mod=3;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
map<char,LL>map1;
LL fac[maxn];
LL ksm(LL a,LL k){
   LL res=1;
   while(k>0){
      if(k&1) res=res*a%mod;
      k>>=1;
      a=a*a%mod;
   }return res%mod;
}
LL C(LL n,LL m){
   if(m>n) return 0;
   return (fac[n]*ksm(fac[m],mod-2)%mod*ksm(fac[n-m],mod-2)%mod)%mod;
}
LL lucas(LL n,LL m){
    if(!m) return 1;
    return C(n%mod,m%mod)*lucas(n/mod,m/mod)%mod;
}
int main(void){
   cin.tie(0);std::ios::sync_with_stdio(false);
   fac[0]=1;
   for(LL i=1;i<=3;i++) fac[i]=fac[i-1]*i%mod;
   map1['B']=0;map1['W']=1;map1['R']=2;
   LL n;cin>>n;
   LL ans=0;
   for(LL i=0;i<n;i++){
      char op;cin>>op;
      LL d=map1[op];
      ans=(ans+d*lucas(n-1,i))%mod;
   }
   if(n%2==0) ans=(3-ans)%3;///ans*=(-1)^(n-1)
   if(ans==0){
      cout<<"B"<<"\n";
   }
   else if(ans==1){
      cout<<"W"<<"\n";
   }
   else if(ans==2){
      cout<<"R"<<"\n";
   }
   return 0;
}
