#include <bits/stdc++.h>
#define ll long long int
#define pb push_back
#define st first
#define nd second
#define pii pair<int,int>
#define mp make_pair
#define pll pair<long long,long long>

using namespace std;

const int nax = 5e5 + 5;
char a[nax];

ll f[nax];
ll inv[nax];

ll nk(ll n, ll k){
    if(n < k) return 0;
    return f[n] / (f[k] * f[n - k]);
}

void prep(){
    f[0] = 1;
    for(int i=1;i<5;i++) f[i] = f[i - 1] * i;
}

vector<int> trojki(int n){
    vector<int> ans;

    while(ans.size() < 15){
        ans.pb(n % 3);
        n /= 3;
    }
    return ans;
}

void solve(){
    int n; cin >> n;
    for(int i=1;i<=n;i++) cin >> a[i];
    int sum = 0;
    int h = n - 1;
    for(int i=0;i<=h;i++){
        int w = 0;
        if(a[i + 1] == 'B') w = 1;
        if(a[i + 1] == 'W') w = 2;
        vector<int> one = trojki(h);
        vector<int> two = trojki(i);
        int c = 1;
        for(int j=0;j<15;j++){
            c *= nk(one[j], two[j]);
            c %= 3;
        }
        sum += c * w;
    }
    sum %= 3;
    if(n % 2 == 0) sum = 3 - sum;
    sum %= 3;
    if(sum == 0) cout <<"R";
    if(sum == 1) cout <<"B";
    if(sum == 2) cout<<"W";



}

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    prep();
    int tt = 1;
    // cin >> tt;
    while(tt--) solve();

    return 0;
}

#include<bits/stdc++.h>
using namespace std;
#define rep(i,x,y) for(int i=(int)(x);i<(int)(y);i++)
#define print(A,x,n) rep(i,0,n){cout<<(i ? " ":"")<<A[i]x;}cout<<endl;
#define pprint(A,y,m,n) rep(j,0,m){print(A[j],y,n);}
const long mod=1e9+7;
const int siz=4e5;
const int inf=1e9;
int fact[siz+1];
int three_count(int n){
	int ret = 0;
	while(n > 0){
		n /= 3;
		ret += n;
	}
	return ret;
}
int modcomb(int n, int r){
	if(three_count(n) > three_count(r) + three_count(n-r)) return 0;
	return (fact[n] * fact[n-r] * fact[r]) % 3;
}
int main(){
	fact[0] = 1;
	rep(i,1,siz+1){
        int j = i;
        while(j % 3 == 0) j /= 3;
		fact[i] = (fact[i-1] * j) % 3;
        //cout<<fact[i]<<endl;
	}
	int N; string s; cin>>N>>s;
	map<char,int> mp1; map<int,char> mp2;
	mp1['B'] = 0; mp1['W'] = 1; mp1['R'] = 2;
	mp2[0] = 'B'; mp2[1] = 'W'; mp2[2] = 'R';
	int ans = 0;
	rep(i,0,N){
        (ans += modcomb(N-1, i) * mp1[s[i]]) %= 3;
        //cout<<modcomb(N-1, i)<<endl;
    }
	if(N % 2 == 0) ans = (3 - ans) % 3;
	cout<<mp2[ans]<<endl;
}