#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 2e5+10;
int to_int(char c) {
	if(c == 'R') return 0;
	if(c == 'W') return 1;
	if(c == 'B') return 2;
	assert(false);
}
char to_char(int x) {
	if(x == 0) return 'R';
	if(x == 1) return 'W';
	if(x == 2) return 'B';
	assert(false);
}
int C(int x, int y) {
	int ans = 1;
	while(x > 0) {
		if(x%3 < y%3) return 0;
		if(y%3 == 1 && x%3 == 2) ans = ans * 2 % 3;
		x /= 3;
		y /= 3;
	}
	return ans;
}
int main() {
	ios::sync_with_stdio(0); cin.tie(0);
	int n;
	string s;
	cin >> n >> s;
	ll ans = 0, pw = 1;
	for(int i = 1; i < n; ++i) {
		pw = pw * 2 % 3;
	}
	for(int i = 0; i < n; ++i) {
		ans += C(n-1, i) * to_int(s[i]) * pw;
		ans %= 3;
	}
	cout << to_char(ans) << endl;
}
#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";
}
