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

int main() {
    int n;
    cin>>n;
    int s=0,p3=0,r3=1;
    for(int i=0;i<n;i++){
        char c;
        cin>>c;
        int x=0;
        if(c=='B')x=1;
        else if(c=='R')x=2;
        if(p3==0)s=(s+x*r3)%3;
        if(i==n-1)break;
        int m=n-1-i;
        while(m%3==0){
            p3++;
            m/=3;
        }
        r3=r3*m%3;
        m=i+1;
        while(m%3==0){
            p3--;
            m/=3;
        }
        r3=r3*m%3;
    }
    if(n%2==0)s=(3-s)%3;
    char ans='W';
    if(s==1)ans='B';
    else if(s==2)ans='R';
    cout<<ans<<endl;
}
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = double;
const int mxn = 4e5+10;
const int mod = 3;

int powmod(int a, int b) {
	int ret = 1;
	while(b) {
		if(b&1) ret*=a, ret%=mod;
		a*=a; a%=mod;
		b>>=1;
	}
	return ret;
}

int c[3][3];

void pre() {
	for(int i=0; i<3; i++) for(int j=0;j<=i; j++) {
		if(j==0) c[i][j] = 1;
		else c[i][j] = (c[i-1][j] + c[i-1][j-1])%mod;
	}  
}

int binom(int n, int k) {
	if(k>n) return 0;
	if(!k) return 1;
	vector<int> bn, bk;
	while(n) {
		bn.push_back(n%3);
		n/=3;
	}
	while(k) {
		bk.push_back(k%3);
		k/=3;
	}
	bn.resize(max(bn.size(), bk.size()), 0);
	bk.resize(max(bn.size(), bk.size()), 0);

	int ret = 1;
	for(int i=0; i<(int)bn.size(); i++) {
		ret*=c[bn[i]][bk[i]];
		ret%=mod;
	}

	return ret;
}



signed main() {
	ios_base::sync_with_stdio(0); cin.tie(0);

	pre();

	int n; cin>>n;
	vector<int> color(n, 0);
	for(int i=0;i<n; i++) {
		char b; cin>>b;
		if(b=='B') color[i] = 0;
		else if(b=='W') color[i] = 1;
		else color[i] = 2;
	}

	int sum = 0;
	for(int i=0; i<n; i++) {
		//cout << "c: " << C(n-1, i) << '\n';
		sum+=binom(n-1, i)*color[i];
		sum%=mod;
	}

	sum*=powmod(2, n-1);
	sum%=mod;

	if(sum==0) {
		cout << "B" << '\n';
	}
	else if(sum==1) {
		cout << "W" << '\n';
	}
	else cout << "R" << '\n';

	return 0;
}
