#include<bits/stdc++.h> 
using namespace std;
const int MOD=3;
const int msize=400005;

int warusan[msize];
int mod3[msize];

void initComb(){
  for(int i=1;i<msize;i++){
    int t=i;
    while(t%3==0){
      t/=3;
      warusan[i]++;
    }
    mod3[i]=t%3;
  }
  for(int i=2;i<msize;i++){
    warusan[i]+=warusan[i-1];
    mod3[i]=mod3[i]*mod3[i-1]%MOD;
  }
}

int comb(int n,int r){
  if(warusan[n]>warusan[r]+warusan[n-r])return 0;
  if((mod3[n]+mod3[r]*mod3[n-r])%3==0)return 2;
  return 1;
}

int main(){
  initComb();
  int n;
  cin>>n;
  vector<short>a(n);
  char t;
  char ans[3]={'R','W','B'};
  for(int i=0;i<n;i++){
    cin>>t;
    switch(t){
      case 'R':a[i]=0;break;
      case 'W':a[i]=1;break;
      case 'B':a[i]=2;break;
    }
  }
  int sum=0;
  for(int i=0;i<n;i++){
    sum=(sum+comb(n-1,i)*a[i])%3;
  }
  if(n%2==0)sum=(3-sum)%3;
  cout<<ans[sum]<<'\n';
}
#include <bits/stdc++.h>
#define inf 0x3f3f3f3f
#define maxm 600005 
#define maxn 150005
#define ls (tot << 1)
#define rs (tot << 1 | 1)
#define PII pair<int, int>
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
const double pi = acos(-1);
const ll mod = 1e9 + 7;
const double eps = 1e-10;
inline ll read(){
    ll x = 0, f = 1;char ch = getchar();
    while(ch > '9' || ch < '0'){if(ch == '-') f = -1;ch = getchar();}
    while(ch >= '0' && ch <= '9'){x = x * 10 + ch -'0';ch = getchar();}
    return x * f;
}
int n;
char s[400005];
int getc(char c){
	if(c == 'B') return 0;
	if(c == 'R') return 1;
	return 2;
}
int c[20][20];
int C(int n, int m){
	if(m > n) return 0;
	if(n <= 3) return c[n][m];
	return C(n / 3, m / 3) * C(n % 3, m % 3);
}
int main(){
	n = read();
	scanf("%s", s);
	int sum = 0;
	int f = 1;
	c[0][0] = 1;
	for(int i = 1;i <= 10;i++){
		c[i][0] = 1;
		for(int j = 1;j <= i;j++){
			c[i][j] = (c[i - 1][j - 1] + c[i - 1][j]) % 3;
		}
	}
	if(n % 2 == 0) f = -1;
	for(int i = 0;i < n;i++){
		sum = (sum + C(n - 1, i) * f * getc(s[i])) % 3;
	}
	sum = sum + 3;
	sum %= 3;
	if(sum == 0) puts("B");
	else if(sum == 1) puts("R");
	else puts("W");
	return 0;
}