#include <bits/stdc++.h>
using namespace std;
#define int long long
const int nax=4e5+10,mod=1e9+7;
char s[nax];
int f[nax],c[nax],n;
int get(int m,int k)
{
    if(c[m]>c[k]+c[m-k])
    return 0;
    return f[m]*f[k]*f[m-k]%3;
}
int32_t main()
{
    int tt=1;
    //cin>>tt;
    while(tt--)
    {
        cin>>n;
        scanf("%s",s+1);
        memset(f,0,sizeof(f));
        memset(c,0,sizeof(c));
        f[0]=1;
        c[0]=0;
        for(int i=1;i<=n;i++)
        {
            int x=i;
            while(x%3==0){
                c[i]++;
                x/=3;
            }
            f[i]=f[i-1]*x%3;
            c[i]+=c[i-1];
        }
        int res=0;
        for(int i=1;i<=n;i++)
        {
            int cur;
            if(s[i]=='B')
            cur=0;
            else if(s[i]=='W')
            cur=1;
            else if(s[i]=='R')
            cur=2;
            int pos=get(n-1,i-1);
            res=(res+pos*cur)%3;
        }
        if(n%2==0)
        res=(-res+3)%3;
        if(res==0)
        cout<<'B';
        else if(res==1)
        cout<<'W';
        else if(res==2)
        cout<<'R';
    }
    return 0;
}
#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
using ll = long long;

const ll MOD = 3;

ll calc_pow(ll x, ll pow) {
    if (pow == 0) return 1;
    ll a = calc_pow(x, pow / 2);
    a = a * a % MOD;
    if (pow % 2 == 1) a *= x;
    return a % MOD;
}

ll calc_div(ll a, ll b) {
    return a * calc_pow(b, MOD - 2) % MOD;
}

vector<ll> fact;

void init_fact(int n) {
    fact = vector<ll>(n);
    fact[0] = 1;
    for (int i = 1; i < n; i++) fact[i] = fact[i - 1] * i % MOD;
}

ll calc_comb(ll n, ll r) {
    if (n < r)return 0;
    return calc_div(fact[n], fact[r] * fact[n - r] % MOD);
}

int main() {
    init_fact(10);

    int n;
    string s;
    cin >> n >> s;

    int ret = 0;
    for (int i = 0; i < n; i++) {
        int times = 1;
        {
            int a = n - 1, b = i;
            while (a > 0) {
                times *= calc_comb(a % 3, b % 3), times %= MOD;
                a /= 3, b /= 3;
            }
        }

        //cout << times << " ";
        if (s[i] == 'W')ret += times * 1;
        if (s[i] == 'R')ret += times * 2;
        ret %= MOD;
    }

    if (ret == 0) cout << "B" << endl;
    else if (ret % 2 == n % 2) cout << "W" << endl;
    else cout << "R" << endl;
    return 0;
}
