#include<bits/stdc++.h>
#define LL long long
using namespace std;
int Len,fact[400010];
char str[400010];
LL ans,KSM[5][400010],f[400010],g[400010];
LL crt_m[1010],crt_r[1010],crt_cnt;
inline int read()
{
	int x=0;bool w=0;char ch=0;
	while(!isdigit(ch)){w|=ch=='-';ch=getchar();}
	while(isdigit(ch)){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
	return w?-x:x;
}
LL ksm(LL B,LL K,LL P,LL A=1)
{
	for(;K;K>>=1,B=B*B%P)
	if(K&1)A=A*B%P;
	return A%P;
}
LL G(LL N,LL P)
{
	if(g[N]!=-1)return g[N];
	return g[N]=(N<P?0:N/P+G(N/P,P));
}
LL F(LL N,LL P,LL PK,LL A=1)
{
	if(f[N]!=-1)return f[N];
	if(!N)return f[N]=1;
	return f[N]=KSM[fact[PK]][N/PK]*fact[N%PK]%PK*F(N/P,P,PK)%PK;
}
LL C_pk(LL N,LL M,LL P,LL PK)
{
	LL fz=F(N,P,PK),fm1=F(M,P,PK),fm2=F(N-M,P,PK);
	return fz*fm1%PK*fm2%PK*(G(N,P)-G(M,P)-G(N-M,P)==0)%PK;
}
int main()
{
	fact[0]=1;
	memset(g,-1,sizeof g);
	memset(f,-1,sizeof f);
	for(int i=1;i<=3;i++)
	if(i%3)fact[i]=fact[i-1]*i%3;
	else fact[i]=fact[i-1];
	KSM[0][0]=KSM[1][0]=KSM[2][0]=1;
	for(int i=1;i<=400000;i++){
		KSM[1][i]=1;
		KSM[2][i]=KSM[2][i-1]*2%3;
	}
	Len=read();
	scanf("%s",str+1);
	for(int i=1;i<=Len;i++)
	if(str[i]=='B')ans=(ans+C_pk(Len-1,i-1,3,3)*0)%3;
	else if(str[i]=='W')ans=(ans+C_pk(Len-1,i-1,3,3)*1)%3;
	else ans=(ans+C_pk(Len-1,i-1,3,3)*2)%3;
	if(Len%2==0)ans=(-ans+3)%3;
	if(ans==0)printf("B\n");
	else if(ans==1)printf("W\n");
	else printf("R\n");
	return 0;
}
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
int comb[10][10];
int lucas (int n, int k) {
  int res = 1;
  while (n > 0) {
    res *= comb[n % 3][k % 3];
    n /= 3;
    k /= 3;
    res %= 3;
  }
  return res;
}
signed main() { 
  ios::sync_with_stdio(false); cin.tie(0);
  comb[0][0] = 1;
  for (int i = 1; i < 4; i++) {
    for (int j = 0; j <= i; j++) {
      comb[i][j] = comb[i - 1][j];
      if (j > 0) comb[i][j] += comb[i - 1][j - 1];
    }
  }
  int n;
  cin >> n;
  string s;
  cin >> s;
  int res = 0;
  for (int i = 0; i < n; i++) {
    int c = 0;
    if (s[i] == 'R') c = 0;
    if (s[i] == 'W') c = 1;
    if (s[i] == 'B') c = 2;
    res += c * lucas(n - 1, i);
    res %= 3;
  }
  if (n % 2 == 0) res = (3 - res) % 3;
  cerr << res << endl;
  if (res == 0) cout << 'R';
  if (res == 1) cout << 'W';
  if (res == 2) cout << 'B';
  cout << endl;
  return 0;
}