#include<bits/stdc++.h>
using namespace std;
int C[3][3] = {{1,0,0}, {1,1,0}, {1,2,1}}; 
int Lucas(int X, int M){
	int XX[20] = {}; 
	int MM[20] = {};
	int x = X; int m = M;
	int ans = 1;   
	for(int i = 0; i < 15; i++){
		XX[i] = x % 3; x /= 3; 
		MM[i] = m % 3; m /= 3;
		ans *= C[XX[i]][MM[i]];
		ans %= 3; 
	}
	return ans; 
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	int N; cin >> N; 
	string S; cin >> S; 
	int A[400010];
	int res = 0;  
	for(int i = 0; i < N; i++){
		if(S[i] == 'B') A[i] = 0; 
		if(S[i] == 'W') A[i] = 1; 
		if(S[i] == 'R') A[i] = 2; 
		res += A[i] * Lucas(N-1, i) % 3; 
		res %= 3; 	
	}
	if(N % 2 == 0){
		res = 3 - res; res %= 3; 
	}
	if(res == 0) cout << "B\n"; 
	if(res == 1) cout << "W\n"; 
	if(res == 2) cout << "R\n"; 
}
#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');

}


