#include <bits/stdc++.h>
using namespace std;
string s;
long long cmp(string s2) {
  long long c = 0;
  for (long long i = 0; i < s.size(); i++) {
    if (s[i] != s2[i]) c++;
  }
  return c;
}
int main() {
  long long n;
  cin >> n;
  cin >> s;
  string s1 = "", s2 = "", s3 = "", s4 = "", s5 = "", s6 = "";
  for (long long i = 0; i < n; i++) {
    switch (i % 3) {
      case 0: {
        s1 += 'R';
        s2 += 'R';
        s3 += 'G';
        s4 += 'G';
        s5 += 'B';
        s6 += 'B';
        break;
      }
      case 1: {
        s1 += 'G';
        s2 += 'B';
        s3 += 'R';
        s4 += 'B';
        s5 += 'R';
        s6 += 'G';
        break;
      }
      case 2: {
        s1 += 'B';
        s2 += 'G';
        s3 += 'B';
        s4 += 'R';
        s5 += 'G';
        s6 += 'R';
        break;
      }
    }
  }
  long long q1 = cmp(s1);
  long long q2 = cmp(s2);
  long long q3 = cmp(s3);
  long long q4 = cmp(s4);
  long long q5 = cmp(s5);
  long long q6 = cmp(s6);
  long long q = min(q1, min(q2, min(q3, min(q4, min(q5, q6)))));
  cout << q << endl;
  if (q == q1)
    cout << s1;
  else {
    if (q == q2)
      cout << s2;
    else {
      if (q == q3)
        cout << s3;
      else {
        if (q == q4)
          cout << s4;
        else {
          if (q == q5)
            cout << s5;
          else
            cout << s6;
        }
      }
    }
  }
  cout << endl;
  return 0;
}
