#include <bits/stdc++.h>
using namespace std;
const long long mod = 4000000;
long long wen[9000000], c[20];
int len, n, a[20][20], boo[20], nex[9000000], hea[9000000];
double val[9000000];
void add(long long x, double y) {
  ++len;
  nex[len] = hea[x % mod];
  wen[len] = x;
  val[len] = y;
  hea[x % mod] = len;
}
int findhash(long long x) {
  for (int i = hea[x % mod]; i; i = nex[i])
    if (wen[i] == x) return i;
  return -1;
}
long long gethash() {
  long long Hash = a[n][1] * 16 + a[n][2] * 4 + a[n][3];
  ;
  if (a[n][1] > a[n][3]) Hash = a[n][3] * 16 + a[n][2] * 4 + a[n][1];
  for (int i = 1; i < n; i++) {
    c[i] = 0;
    if (boo[i] == 1 || (boo[i] == 2 && a[i][2] == 0)) continue;
    int x = a[i][1], y = a[i][2], z = a[i][3];
    if (x > z) swap(x, z);
    c[i] = x * 16 + y * 4 + z;
  }
  sort(c + 1, c + n);
  for (int i = 1; i < n; i++)
    if (c[i] != 0) Hash = Hash * 67 + c[i];
  return Hash;
}
double dp() {
  int p = 1;
  long long Hash = gethash(), HASH = findhash(Hash);
  if (HASH >= 0) return val[HASH];
  double b[4] = {0, 100000000, 100000000, 100000000};
  for (int k = 1; k <= 3; k++)
    for (int i = 1; i < n; i++)
      for (int j = 1; j <= 3; j++)
        if (a[i][j] == k &&
            (boo[i] == 3 || (boo[i] == 2 && a[i][2] > 0 && j != 2))) {
          if (boo[n] == 3) ++n;
          ++boo[n];
          --boo[i];
          a[i][j] = 0;
          for (int ij = 1; ij <= 3; ij++)
            if (!a[n][ij]) {
              a[n][ij] = k;
              b[k] = min(b[k], dp());
              a[n][ij] = 0;
            }
          a[i][j] = k;
          ++boo[i];
          --boo[n];
          if (boo[n] == 0) --n;
        }
  if (b[1] == 100000000 && b[2] == 100000000 && b[3] == 100000000) return 0;
  if (b[1] == 100000000) b[1] = 0, p += 2;
  if (b[2] == 100000000) b[2] = 0, p += 2;
  if (b[3] == 100000000) b[3] = 0, p += 1;
  double ans = 1 + b[1] / 3 + b[2] / 3 + b[3] / 6;
  ans = ans * 6.0 / (6 - p);
  if (findhash(Hash) == -1) add(Hash, ans);
  return ans;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    boo[i] = 3;
    char s[4];
    scanf("%s", s);
    for (int j = 1; j <= 3; j++) {
      if (s[j - 1] == 'B') a[i][j] = 2;
      if (s[j - 1] == 'G') a[i][j] = 1;
      if (s[j - 1] == 'R') a[i][j] = 3;
    }
  }
  printf("%.10lf", dp());
}
