#include <cstdio>
const int Maxn=400000;
int fac[Maxn+5],num[Maxn+5],inv_f[Maxn+5],inv_n[Maxn+5];
void init(){
	fac[0]=1;
	for(int i=1;i<=Maxn;i++){
		fac[i]=fac[i-1],num[i]=num[i-1];
		int x=i;
		while(x%3==0){
			x/=3;
			num[i]++;
		}
		fac[i]=1ll*fac[i-1]*x%3;
	}
	inv_f[Maxn]=fac[Maxn],inv_n[Maxn]=num[Maxn];
	for(int i=Maxn-1;i>=0;i--){
		int x=i+1;
		inv_f[i]=inv_f[i+1],inv_n[i]=inv_n[i+1];
		while(x%3==0){
			x/=3;
			inv_n[i]--;
		}
		inv_f[i]=1ll*inv_f[i+1]*x%3;
	}
}
int C(int n,int m){
	if(num[n]-inv_n[m]-inv_n[n-m]!=0){
		return 0;
	}
	return fac[n]*inv_f[m]*inv_f[n-m]%3;
}
char s[Maxn+5];
int main(){
	init();
	int n;
	scanf("%d",&n);
	scanf("%s",s+1);
	int ans=0;
	for(int i=1;i<=n;i++){
		int val=(s[i]=='B'?0:(s[i]=='W'?1:2));
		ans=(ans+1ll*C(n-1,i-1)*val)%3;
	}
	if(ans==0){
		putchar('B');
	}
	else if((ans&1)^(n&1)){
		putchar('R');
	}
	else{
		putchar('W');
	}
	return 0;
}

using namespace std;
#include <bits/stdc++.h>
#define N 400005
#define ll long long
int n;
char str[N];
int c[3][3];
int C(int m,int n){
//	if (m<n) return 0;
//	return fac[m]*ifac[n]%mo*ifac[m-n]%mo;
	if (m<3 && n<3)
		return c[m][n];
	return C(m/3,n/3)*C(m%3,n%3);
}
int id[255];
int re[3]={'B','W','R'};
int main(){
//	freopen("in.txt","r",stdin);
	scanf("%d%s",&n,str);
	for (int i=0;i<3;++i){
		c[i][0]=1;
		for (int j=1;j<3;++j)
			c[i][j]=(c[i-1][j-1]+c[i-1][j])%3;
	}
	int ans=0;
	id['B']=0,id['W']=1,id['R']=2;
	for (int i=0;i<n;++i)
		ans+=id[str[i]]*C(n-1,i);
	if (n-1&1) ans*=-1;
	ans=(ans%3+3)%3;
	printf("%c\n",re[ans]);
	return 0;
}
