#include <bits/stdc++.h>   using namespace std;   const double pi = acos(-1);   const int dx[4] = {0, 0, 1, -1};   const int dy[4] = {1, -1, 0, 0};   int n, a, b, c;   string s;   map<pair<int, pair<int, int> >, int> dic;   bool bo1 = false, bo2 = false, bo3 = false;   void dfs(int a, int b, int c) {     pair<int, pair<int, int> > temp = make_pair(a, make_pair(b, c));     if (dic[temp]) return;     dic[temp] = 1;     if (a + b + c == 1) {       if (a == 1) bo1 = true;       if (b == 1) bo2 = true;       if (c == 1) bo3 = true;       return;     }     if (a > 0 && b > 0) dfs(a - 1, b - 1, c + 1);     if (a > 0 && c > 0) dfs(a - 1, b + 1, c - 1);     if (b > 0 && c > 0) dfs(a + 1, b - 1, c - 1);     if (a > 1) dfs(a - 1, b, c);     if (b > 1) dfs(a, b - 1, c);     if (c > 1) dfs(a, b, c - 1);   }   int main() {     ios::sync_with_stdio(0), cin.tie(0);     cin >> n;     cin >> s;     for (int i = 0; i < (int)s.size(); i++) {       if (s[i] ==  B ) a++;       if (s[i] ==  G ) b++;       if (s[i] ==  R ) c++;     }     dfs(a, b, c);     if (bo1) cout <<  B ;     if (bo2) cout <<  G ;     if (bo3) cout <<  R ;     return 0;   }   