#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline bool upmin(T &x, T y) {
  return y < x ? x = y, 1 : 0;
}
template <typename T>
inline bool upmax(T &x, T y) {
  return x < y ? x = y, 1 : 0;
}
const long double eps = 1e-6;
const long double pi = acos(-1);
const int oo = 1 << 30;
const long long loo = 1ll << 62;
const int mods = 1e7 + 9;
const int MAXN = 6000005;
const int MX = 1e7 + 50;
const int INF = 0x3f3f3f3f;
inline int read() {
  int f = 1, x = 0;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = (x << 3) + (x << 1) + (c ^ 48);
    c = getchar();
  }
  return x * f;
}
int num = 0;
pair<unsigned long long, double> g[MAXN];
int nxt[MAXN], head[MX], nodenum = 0;
void insert(int x, unsigned long long y, double z) {
  nxt[++nodenum] = head[x], g[nodenum] = make_pair(y, z), head[x] = nodenum;
}
double query(unsigned long long x) {
  for (int i = head[x % mods]; i; i = nxt[i])
    if (g[i].first == x) return g[i].second;
  return -1;
}
struct Hash_Node {
  int n;
  unsigned long long h;
  struct Node {
    int x, y, z;
  } a[18];
  void Init() {
    int b[18];
    for (int i = 0; i < n; i++) {
      if (a[i].x > a[i].z) swap(a[i].x, a[i].z);
      b[i] = (a[i].y && (a[i].x || a[i].z) || i == n - 1)
                 ? (a[i].x << 4) + (a[i].y << 2) + a[i].z
                 : 0;
    }
    sort(b, b + n - 1), h = 0;
    for (int i = 0; i < n; i++) h = (h << 6) + (h << 1) + h + b[i];
  }
} fst;
double dfs(Hash_Node nw) {
  nw.Init();
  double tmp = query(nw.h);
  if (tmp != -1) return tmp;
  num++;
  double P = 5.0 / 6, ans = 1;
  int flag = 0;
  if (nw.a[nw.n - 1].x && nw.a[nw.n - 1].y && nw.a[nw.n - 1].z)
    nw.n++, flag = 1;
  for (int p = 1; p <= 3; p++) {
    int Flag = 0;
    double t = INF, q;
    for (int i = 0; i < nw.n - 1 - flag; i++) {
      if (nw.a[i].x == p && nw.a[i].y && !nw.a[nw.n - 1].x)
        nw.a[i].x = 0, nw.a[nw.n - 1].x = p, q = dfs(nw), upmin(t, q),
        nw.a[nw.n - 1].x = 0, nw.a[i].x = p, Flag = 1;
      else if (nw.a[i].z == p && nw.a[i].y && !nw.a[nw.n - 1].x)
        nw.a[i].z = 0, nw.a[nw.n - 1].x = p, q = dfs(nw), upmin(t, q),
        nw.a[nw.n - 1].x = 0, nw.a[i].z = p, Flag = 1;
      if (nw.a[i].x == p && nw.a[i].y && !nw.a[nw.n - 1].y)
        nw.a[i].x = 0, nw.a[nw.n - 1].y = p, q = dfs(nw), upmin(t, q),
        nw.a[nw.n - 1].y = 0, nw.a[i].x = p, Flag = 1;
      else if (nw.a[i].z == p && nw.a[i].y && !nw.a[nw.n - 1].y)
        nw.a[i].z = 0, nw.a[nw.n - 1].y = p, q = dfs(nw), upmin(t, q),
        nw.a[nw.n - 1].y = 0, nw.a[i].z = p, Flag = 1;
      if (nw.a[i].y == p && nw.a[i].x && nw.a[i].z && !nw.a[nw.n - 1].x)
        nw.a[i].y = 0, nw.a[nw.n - 1].x = p, q = dfs(nw), upmin(t, q),
        nw.a[nw.n - 1].x = 0, nw.a[i].y = p, Flag = 1;
      if (nw.a[i].y == p && nw.a[i].x && nw.a[i].z && !nw.a[nw.n - 1].y)
        nw.a[i].y = 0, nw.a[nw.n - 1].y = p, q = dfs(nw), upmin(t, q),
        nw.a[nw.n - 1].y = 0, nw.a[i].y = p, Flag = 1;
    }
    if (!Flag)
      P -= (p == 1 ? (1.0 / 6) : (1.0 / 3));
    else
      ans += (p == 1 ? t / 6 : t / 3);
  }
  if (flag) nw.n--;
  ans = (P < eps ? 0 : ans / P), insert(nw.h % mods, nw.h, ans);
  return ans;
}
signed main() {
  int n;
  n = fst.n = read();
  for (int i = 0; i < n; i++) {
    char st[5];
    scanf("%s", st);
    fst.a[i].x = (st[0] <= 'B') + (st[0] <= 'G') + (st[0] <= 'R');
    fst.a[i].y = (st[1] <= 'B') + (st[1] <= 'G') + (st[1] <= 'R');
    fst.a[i].z = (st[2] <= 'B') + (st[2] <= 'G') + (st[2] <= 'R');
  }
  printf("%.20lf\n", dfs(fst));
  return 0;
}
