#include <bits/stdc++.h>
using namespace std;
bool dp[202][202][202];
int n, i, j, k;
bool vis[3];
string s, ans = "";
int g, b, r;
void rec(int blue, int green, int red) {
  if (blue + green + red <= 1) {
    if (blue && !vis[0]) {
      ans += "B";
      vis[0] = true;
    }
    if (green && !vis[1]) {
      ans += "G";
      vis[1] = true;
    }
    if (red && !vis[2]) {
      ans += "R";
      vis[2] = true;
    }
    return;
  }
  if (dp[blue][green][red]) return;
  if (blue >= 2) rec(blue - 1, green, red);
  if (green >= 2) rec(blue, green - 1, red);
  if (red >= 2) rec(blue, green, red - 1);
  if (blue >= 1 && green >= 1) rec(blue - 1, green - 1, red + 1);
  if (blue >= 1 && red >= 1) rec(blue - 1, green + 1, red - 1);
  if (green >= 1 && red >= 1) rec(blue + 1, green - 1, red - 1);
  dp[blue][green][red] = true;
}
int main() {
  cin >> n;
  cin >> s;
  for (i = 0; i < n; i++) {
    if (s[i] == 'R')
      r++;
    else if (s[i] == 'G')
      g++;
    else
      b++;
  }
  rec(b, g, r);
  sort(ans.begin(), ans.end());
  cout << ans << endl;
}
