#include <bits/stdc++.h>
using namespace std;
bool ex[3];
bool dp[201][201][201];
void solve(int b, int g, int r) {
  if (b + g + r == 1) {
    if (g)
      ex[1] = 1;
    else if (r)
      ex[2] = 1;
    else
      ex[0] = 1;
    return;
  }
  if (dp[b][g][r]) return;
  dp[b][g][r] = true;
  if (b >= 2) solve(b - 1, g, r);
  if (g >= 2) solve(b, g - 1, r);
  if (r >= 2) solve(b, g, r - 1);
  if (r && g) solve(b + 1, g - 1, r - 1);
  if (b && g) solve(b - 1, g - 1, r + 1);
  if (b && r) solve(b - 1, g + 1, r - 1);
}
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  int r = 0, g = 0, b = 0;
  for (int i = 0; i < n; ++i) {
    if (s[i] == 'R')
      r++;
    else if (s[i] == 'G')
      g++;
    else
      b++;
  }
  solve(b, g, r);
  if (ex[0]) cout << "B";
  if (ex[1]) cout << "G";
  if (ex[2]) cout << "R";
  cout << endl;
}
