/*
Author: QAQAutoMaton
Lang: C++
Code: C.cpp
Mail: lk@qaq-am.com
Blog: https://www.qaq-am.com/
*/
#include<bits/stdc++.h>
#define debug(qaq...) fprintf(stderr,qaq)
#define DEBUG printf("Passing [%s] in LINE %d\n",__FUNCTION__,__LINE__)
#define Debug debug("Passing [%s] in LINE %d\n",__FUNCTION__,__LINE__)
#define all(x) x.begin(),x.end()
#define x first
#define y second
#define unq(a) sort(all(a)),a.erase(unique(all(a)),a.end())
using namespace std;
typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef complex<double> cp;
typedef pair<int,int> pii;
int inf;
const double eps=1e-8;
const double pi=acos(-1.0);
template<class T,class T2>int chkmin(T &a,T2 b){return a>b?a=b,1:0;}
template<class T,class T2>int chkmax(T &a,T2 b){return a<b?a=b,1:0;}
template<class T>T sqr(T a){return a*a;}
template<class T,class T2>T mmin(T a,T2 b){return a<b?a:b;}
template<class T,class T2>T mmax(T a,T2 b){return a>b?a:b;}
template<class T>T aabs(T a){return a<0?-a:a;}
template<class T>int dcmp(T a,T b){return a>b;}
template<int *a>int cmp_a(int x,int y){return a[x]<a[y];}
template<class T>bool sort2(T &a,T &b){return a>b?swap(a,b),1:0;}
#define min mmin
#define max mmax
#define abs aabs
struct __INIT__{
	__INIT__(){
		fill((unsigned char*)&inf,(unsigned char*)&inf+sizeof(inf),0x3f);
	}
}__INIT___;
namespace io {
	const int SIZE = (1 << 21) + 1;
	char ibuf[SIZE], *iS, *iT, obuf[SIZE], *oS = obuf, *oT = oS + SIZE - 1, c, qu[55]; int f, qr;
	// getchar
	#define gc() (iS == iT ? (iT = (iS = ibuf) + fread (ibuf, 1, SIZE, stdin), (iS == iT ? EOF : *iS ++)) : *iS ++)
	// print the remaining part
	inline void flush () {
		fwrite (obuf, 1, oS - obuf, stdout);
		oS = obuf;
	}
	// putchar
	inline void putc (char x) {
		*oS ++ = x;
		if (oS == oT) flush ();
	}
	template<typename A>
	inline bool read (A &x) {
		for (f = 1, c = gc(); c < '0' || c > '9'; c = gc()) if (c == '-') f = -1;else if(c==EOF)return 0;
		for (x = 0; c <= '9' && c >= '0'; c = gc()) x = x * 10 + (c & 15); x *= f;
		return 1;
	}
	inline bool read (char &x) {
		while((x=gc())==' '||x=='\n' || x=='\r');
		return x!=EOF;
	}
	inline bool read(char *x){
		while((*x=gc())=='\n' || *x==' '||*x=='\r');
		if(*x==EOF)return 0;
		while(!(*x=='\n'||*x==' '||*x=='\r'||*x==EOF))*(++x)=gc();
		*x=0;
		return 1;
	}
	template<typename A,typename ...B>
	inline bool read(A &x,B &...y){
		return read(x)&&read(y...);
	}
	template<typename A>
	inline bool write (A x) {
		if (!x) putc ('0'); if (x < 0) putc ('-'), x = -x;
		while (x) qu[++ qr] = x % 10 + '0',  x /= 10;
		while (qr) putc (qu[qr --]);
		return 0;
	}
	inline bool write (char x) {
		putc(x);
		return 0;
	}
	inline bool write(const char *x){
		while(*x){putc(*x);++x;}
		return 0;
	}
	inline bool write(char *x){
		while(*x){putc(*x);++x;}
		return 0;
	}
	template<typename A,typename ...B>
	inline bool write(A x,B ...y){
		return write(x)||write(y...);
	}
	//no need to call flush at the end manually!
	struct Flusher_ {~Flusher_(){flush();}}io_flusher_;
}
using io :: read;
using io :: putc;
using io :: write;
char a[400005];
const int c3[3][3]={{1,0,0},{1,1,0},{1,2,1}};
int C(int a,int b){
	if(!b)return 1;
	if(!a)return 0;
	return c3[a%3][b%3]*C(a/3,b/3)%3;
}
signed main(){
#ifdef QAQAutoMaton 
	freopen("C.in","r",stdin);
	freopen("C.out","w",stdout);
#endif
	int n;	
	read(n);
	read(a);
	int s=0;
	for(int i=0;i<n;++i){
		s+=C(n-1,i)*(a[i]=='B'?0:a[i]=='W'?1:2);
		s%=3;
	}
	if((n-1)&1)s=(3-s)%3;
	write("BWR"[s],'\n');
	return 0;
}


#include<bits/stdc++.h>
#define inf 1e18
#define endl "\n"
#define mp make_pair
#define pb push_back
#define loop(i,x,y) for(int i = x; i < y ; i++ )
#define all(x) (x).begin(),(x).end()
#define in(n)       int n; cin>>n;
#define inarr(arr,n) vector<int>arr(n); for(int i = 0; i < n ; i++){cin>>arr[i];}
#define maploop(x) for(auto itr = x.begin(); itr != x.end();itr++)
#define int long long
using namespace std;
#ifndef ONLINE_JUDGE
#define debug(x) cerr << #x<<" "; _print(x); cerr << endl;
#else
#define debug(x);
#endif

void _print(int t) {cerr << t;}
void _print(string t) {cerr << t;}
void _print(char t) {cerr << t;}
void _print(double t) {cerr << t;}


template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);
template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);
template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p) {cerr << "{"; _print(p.first); cerr << ","; _print(p.second); cerr << "}";}
template <class T> void _print(vector <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(set <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(multiset <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void _print(map <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}
/*-------------------------------------------------------------------------------------------------------------------------------------------------------------------*/


const int N = 5;
const int mod = 3;
int fac[N];
int mul(int a, int b)
{
	return (a * b) % mod;
}
void pre()
{
	fac[0] = 1;
	loop(i, 1, N)
	{

		fac[i] = mul(fac[i - 1], i);
	}
}
int sub(int a, int b)
{
	int l = a - b;
	if (l < 0)
	{
		l += mod;
	}
	return l;
}
int pow(int a, int b)
{
	int z = 1;
	while (b  > 0 )
	{
		if (b % 2)
		{
			z = mul(a, z);
		}
		a = mul(a, a);
		b = b / 2;

	}
	return z;
}
int div(int a)
{
	int ans;
	return ans = pow(a, mod - 2);
}
int comb(int n, int k)
{
	if (n >= k)
	{
		return mul(fac[n], div(mul(fac[k], fac[n - k])));
	}
	else
		return 0;
}
int add(int a, int b)
{
	a += b;
	if (a > mod)
	{

		a -= mod;
	}
	return a;
}
int solve(int n, int k)
{
	int ans = 1;
	while (n > 0)
	{
		ans = ans * comb(n % 3, k % 3);
		n /= 3;
		k /= 3;
	}
	return ans;
}
void Main()
{

	in(n)
	string s;
	cin >> s;
	vector<int>arr(n);
	loop(i, 0, n)
	{
		if (s[i] == 'R')
			arr[i] = 0;
		else if (s[i] == 'B')
			arr[i] = 1;
		else
			arr[i] = 2;
	}
	//debug(arr)
	int l = n - 1;
	int ans = 0;
	loop(i, 0, n)
	{
		int l = mul(arr[i], solve((n - 1), i));
		l %= 3;
		ans = add(ans, l);
		debug(ans)
	}
	loop(i, 1, n)
	{
		if (ans % 2) ans += 3;
		ans /= 2;
	}
	if (l % 2)
	{
		debug(ans)
		// ans *= -1;

		// if (ans < 0)
		// {
		// 	ans += 3;
		// }

		if (ans == 2)
		{
			cout << "W" << endl;
		}
		else if (ans == 1)
			cout << "B" << endl;
		else
			cout << "R" << endl;
	}
	else
	{
		//ans %= 3;
		debug(ans)
		if (ans == 2)
		{
			cout << "W" << endl;
		}
		else if (ans == 1)
			cout << "B" << endl;
		else
			cout << "R" << endl;
	}




}






int32_t main()
{
	pre();
	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	//usaco("runround");
	int t = 1;
	//cin >> t;
	//t = 10000;
	for (int i = 1; i <= t; i++)
	{
		//cout << "Case #" << i << ": ";
		Main();
	}
}