#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]);
}
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(x,y,z) for(int x=y;x<=z;x++)
const int N=4e5+10;
const double eps = 0.01;
const ll mod = 1e9+7;
const double pi = acos(-1.0) ;
const ll inf = 0x3f3f3f3f3f3f3f3f;
const ll DIV=100000;
inline ll read()
{
    ll x=0,f=1;char ch=getchar();
    while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}
    while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
    return x*f;
}
inline void pt(ll ans,ll f){
    printf("%lld",ans);
    if(f==1) putchar(' ');
    else putchar('\n');
}
ll n,m,k,tot;
ll f[N],g[N];
string str;
int main() {
//    scanf("%d%d", &n, &m);
    int q;
    f[1]=0,g[1]=g[0]=1;
    for(int i=2;i<N;i++){
        int cnt=0,tmp=i;
        while(tmp%3==0){
            tmp/=3;
            cnt++;
        }
        f[i]=f[i-1]+cnt;
        g[i]=g[i-1]*tmp%3;
    }
    n = read();
    cin>>str;
    int len=str.length();
    ll ans=0;
    for(int i=0;i<len;i++){
//        cout<<f[i]<<":"<<g[i]<<endl;
        if(str[i]=='W') ans=ans+(f[n-1]-f[i]-f[n-1-i]==0)*g[n-1]*g[i]*g[n-1-i]%3;
        else if(str[i]=='R') ans=ans+2*(f[n-1]-f[i]-f[n-1-i]==0)*g[n-1]*g[i]*g[n-1-i]%3;
//        pt(ans,2);
        ans%=3;
    }
//    cout<<ans<<endl;
    if(n%2==0) ans=(-ans+3)%3;
    if(ans==0) putchar('B');
    else if (ans == 1 ) putchar('W');
    else putchar('R');
    return 0;
}