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

int main(){
  long long n;
  cin >> n;
  string c;
  cin >> c;
  
  int a[n+1];
  
  for(int i=0;i<n;i++){
    if(c[i] == 'R'){
      a[i] = 0;
    }
    
    if(c[i] == 'B'){
      a[i] = 1;
    }
    
    if(c[i] == 'W'){
      a[i] = 2;
    }
  }
  
  int ord3[n+1];
  ord3[0]=0;
  
  for(int i=1;i<=n;i++){
    int k=i;
    for(int j=1;j>=0;j++){
      if(k%3 != 0){
        ord3[i]=j-1;
        break;
      }
      k/=3;
    }
  }
  
  int fact[n+1];
  int fact_ord3[n+1];
  
  fact[0]=1;
  fact[1]=1;
  fact_ord3[1]=0;
  fact_ord3[0]=0;
  
  for(int i=2;i<=n;i++){
    fact_ord3[i]=fact_ord3[i-1]+ord3[i];
    if(i%3 == 0){
      int k=i;
      for(int j=1;j>=0;j++){
        if(k%3!=0)break;
        k/=3;
      }
      fact[i]=fact[i-1]*k;
      fact[i]%=3;
      continue;
    }
    fact[i] = fact[i-1]*i ;
    fact[i]%=3;
  }
  
  int comb[n+1];
  
  for(int i=0;i<n;i++){
    if(fact_ord3[n-1] > fact_ord3[i]+fact_ord3[n-i-1]){
      comb[i]=0;
      continue;
    }
    comb[i] = fact[n-1] * fact[i] * fact[n-i-1];
    comb[i] %= 3;
  }
  
  int ans = 0;
  for(int i=0;i<n;i++){
    ans += a[i] *comb[i];
    ans %= 3;
  }
  
  if(n%2==0){
    ans *= -1;
  }
  
  if(ans < 0)ans += 3;
  
  if(ans==1){
    cout << "B" ;
    return 0;
  }
  
  if(ans == 0){
    cout << "R";
    return 0;
  }
  
  cout << "W";
  return 0;
  
}
#include <bits/stdc++.h>
#define int int
#define maxn 800005
#define mod 3
using namespace std;
int n;
char r[maxn];
char get_char(){
    char ch = getchar();
    while(ch != 'W' && ch != 'B' && ch != 'R')    ch = getchar();
    return ch;
}
int jc[maxn], inv[maxn];
int qpow(int a, int b, int p){
    if(b == 0)    return 1;
    int tmp = qpow(a, b / 2, p);
    tmp = (tmp * tmp) % p;
    if(b & 1)   tmp = (tmp * a) % p;
    return tmp;
}
void get_jc(){
    jc[0] = 1;
    for(int i = 1; i <= n; i++)
        jc[i] = (jc[i - 1] * i);
}
int C(int a, int b, int p) {
    if (b < a)    return 0;
    int s = jc[a] * jc[b - a] % p;
    return jc[b] * qpow(s, p - 2, p) % p;
}

int lucas(int x, int y, int p) {
    if (x == 0)    return 1;
    return lucas(x / p, y / p, p) * C(x % p, y % p, p) % p;
}

int tra(char ch){
    //putchar(ch);
    if(ch == 'B')    return 1;
    if(ch == 'W')    return 2;
    if(ch == 'R')    return 0;
    return -1;
}
signed main(void)
{   
    scanf("%lld", &n);
    for(int i = 1; i <= n; i++)
        r[i] = get_char();
    get_jc();
    int res = 0;
    for(int i = 0; i <= n - 1; i++)
    {
        res = (res + tra(r[i + 1]) * lucas(i, n - 1, mod)) % mod;
        //printf("%d\n", res);
    }
    if((n + 1) & 1)
        res = -res;
    res = ((res % mod) + mod) % mod;
    if(res == 1)
        printf("B\n");
    else if(res == 2)
        printf("W\n");
    else
        printf("R\n");
    return 0;
}
