# include <bits/stdc++.h>
using namespace std;

const int maxn=4000000+5;
map<pair<int,int>,int> P;
int c[15][15]={{1,0,0,0,0},{1,1,0,0,0},{1,2,1,0,0},{1,3,3,1,0},{0,0,0,0,0},{0,0,0,0,0}};
int n;
char s[maxn];

int lucas(int a,int b){
    pair<int,int> d(a,b);
    if(P[d]!=0) return P[{a,b}];
    return P[d]=(b>0?(lucas(a/3,b/3)*c[a%3][b%3]%3):1);
}

int main(){
    ios::sync_with_stdio(false);
    cin>>n>>s;
    int fl=(n%2?1:-1);
    int res=0;
    for(int i=0;i<n;i++){
        int p;
        if(s[i]=='B') p=0;
        if(s[i]=='R') p=1;
        if(s[i]=='W') p=2;
        res=(res+fl*p*lucas(n-1,i))%3;
        res=(res+3)%3;
    }
    if(res==0) cout<<"B";
    else if(res==1) cout<<"R";
    else cout<<"W";
    return 0;
}

#include<bits/stdc++.h>
using namespace std;

const int N=4e5+1e3+7;

int C(int n,int m)
{
	if(n<m||n<0||m<0)
		return 0;
	long long ret=1;
	for(int i=n;i>=n-m+1;i--)
		ret=ret*i;
	for(int i=1;i<=m;i++)
		ret=ret/i;
	return ret%3;
}

int Lucas(int n,int m)
{
	if(n<3||m<3)
		return C(n,m);
	return C(n%3,m%3)*Lucas(n/3,m/3)%3;
}

int get(char c)
{
	return c=='R'?0:c=='B'?1:2;
}

int n;

char s[N];

string ans="RBW";

int main()
{
	scanf("%d",&n);
	scanf("%s",s);
	n--;
	int r=0;
	for(int i=0;i<=n;i++)
		(r+=Lucas(n,i)*get(s[i]))%=3;
	if(n&1)
		r=(3-r)%3;
	putchar(ans[r]);
}