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

#define int             long long
#define w(x)            int x; cin>>x; while(x--)
#define endl            ("\n")
#define f(i, a, n)      for(int i=a; i<n; i++)
#define cc(r)           cout<<r<<" "
#define ce(r)           cout<<r<<endl



void inout()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

}
int nCrModpDP(int n, int r, int p)
{
    int C[r + 1];
    memset(C, 0, sizeof(C));

    C[0] = 1;
    for (int i = 1; i <= n; i++)
    {
        for (int j = min(i, r); j > 0; j--)
            C[j] = (C[j] + C[j - 1]) % p;
    }
    return C[r];
}

int nCrModpLucas(int n, int r, int p)
{
    if (r == 0)
        return 1;
    int ni = n % p, ri = r % p;
    return (nCrModpLucas(n / p, r / p, p) * nCrModpDP(ni, ri, p)) % p;
}
int32_t main()
{
    inout();
    int n;
    cin >> n;
    int r[n], a[n], ans = 0;
    f(i, 0, n) {
        r[i] = nCrModpLucas(n - 1, i, 3);
    }
    char k;
    f(i, 0, n) {
        cin >> k;
        if (k == 'B')
            a[i] = 0;
        else if (k == 'W')
            a[i] = 1;
        else
            a[i] = 2;
    }
    f(i, 0, n) {
        ans = (ans + (a[i] * r[i]) % 3) % 3;
    }
    if ((n & 1) == 0) {
        ans = (-ans + 3) % 3;
    }
    if (ans == 0)
        ce('B');
    else if (ans == 1)
        ce('W');
    else
        ce('R');

}



#include <bits/stdc++.h>
#define rep(i, a, b)   for(int i = a; i <= b; ++i)
#define repr(i,a,b)    for(int i = a ; i >= b; --i)
#define NAME           "NAME"
#define pb             push_back
#define mp             make_pair
#define EL             cout << '\n'
#define cqtshadow      int main
#define fillchar(a,x)  memset(a, x, sizeof (a))
#define faster         ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
using namespace std;
typedef int64_t        ll;
typedef vector<int>    vi;
typedef vector<ll>     vl;
typedef pair<int, int> ii;
typedef pair<ll, ll>   iil;
const ll  oo  =  1e18;
const int inf =  1e9;
const int mod =  3;
const int N   =  4e5 + 7;
const int M   =  1e6 + 7;
void file() {freopen ( NAME ".inp", "r", stdin ); freopen ( NAME ".out", "w", stdout ); freopen ( NAME ".err", "w", stderr);}

int n, c[N], C_[5][5];
string s;

void cal() {
	rep(i, 0, 3)
	rep(j, 0, i) 
		if(i == 0 || j == 0) C_[i][j] = 1;
		else C_[i][j] = (C_[i - 1][j]%mod + C_[i - 1][j - 1]%mod)%mod;
}		

int C(int k, int n) {
	if(k < mod && n < mod) return C_[n][k];
	return (C(k/mod, n/mod)%mod * C_[n%mod][k%mod])%mod;
}

cqtshadow () {
	faster
	cin >> n >> s;
	rep(i, 1, n) {
		if(s[i - 1] == 'W') c[i] = 0;
		if(s[i - 1] == 'R') c[i] = 1;
		if(s[i - 1] == 'B') c[i] = 2;
	}
	cal();
	int res = 0;
	rep(i, 1, n) {
		res = (res + (c[i] * C(i - 1, n - 1)%mod)%mod)%mod;
	}
	if(n%2 == 0) res *= -1;
	res = (res%mod + mod*1000000)%mod;
	if(res == 0) cout << "W";
	if(res == 1) cout << 'R';
	if(res == 2) cout << "B";
}
