#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int N;
int A[402020];

ll mo=3;

ll fact[403030];
ll fact3[403030];

ll modpow(ll a, ll n=mo-2) {
	ll r=1;
	while(n) r=r*((n%2)?a:1)%mo,a=a*a%mo,n>>=1;
	return r;
}

ll comb(int A,int B) {
	int C=A-B;
	
	if(fact3[A]>fact3[B]+fact3[C]) return 0;
	return fact[A]*modpow(fact[B]*fact[C])%mo;
	
	
}

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	
	fact[0]=1;
	fact3[0]=0;
	for(i=1;i<=N-1;i++) {
		fact[i]=fact[i-1];
		fact3[i]=fact3[i-1];
		x=i;
		while(x%3==0) {
			fact3[i]++;
			x/=3;
		}
		fact[i]=fact[i]*x%3;
	}
	
	
	
	cin>>s;
	ll ret=0;
	FOR(i,N) {
		if(s[i]=='B') A[i]=0;
		if(s[i]=='W') A[i]=1;
		if(s[i]=='R') A[i]=2;
		
		if(N%2==1) {
			ret+=comb(N-1,i)*A[i];
		}
		else {
			ret-=comb(N-1,i)*A[i];
		}
	
	}
	ret=(ret%3+3)%3;
	cout<<"BWR"[ret]<<endl;
	
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}

#include<bits/stdc++.h>
using namespace std;
const int N=400005;
int n,a[N],f[]={1,1,2},sum;
char s[N];
int c(int n,int m)
{
	if(n<m) return 0;
	if(n<3) return f[n]*f[m]*f[n-m]%3;
	return c(n%3,m%3)*c(n/3,m/3)%3;
}
int main()
{
	scanf("%d%s",&n,s+1);
	for(int i=1;i<=n;i++)
		if(s[i]=='W') a[i]=1;
		else if(s[i]=='R') a[i]=2;
	for(int i=1;i<=n;i++) sum=(sum+a[i]*c(n-1,i-1))%3;
	if(n%2==0) sum=(3-sum)%3;
	if(sum==0) puts("B");
	if(sum==1) puts("W");
	if(sum==2) puts("R");
	return 0;
}