#include <bits/stdc++.h>
using namespace std;

typedef long long   signed int LL;
typedef long long unsigned int LU;

#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); i++)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); i--)
#define  inc(i, n) incID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define  dec(i, n) decID(i, 0, n)
#define dec1(i, n) decII(i, 1, n)

#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))

#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define PQ priority_queue

#define  ALL(v)  v.begin(),  v.end()
#define RALL(v) v.rbegin(), v.rend()
#define  FOR(it, v) for(auto it =  v.begin(); it !=  v.end(); ++it)
#define RFOR(it, v) for(auto it = v.rbegin(); it != v.rend(); ++it)

template<typename T> bool   setmin(T & a, T b) { if(b <  a) { a = b; return true; } else { return false; } }
template<typename T> bool   setmax(T & a, T b) { if(b >  a) { a = b; return true; } else { return false; } }
template<typename T> bool setmineq(T & a, T b) { if(b <= a) { a = b; return true; } else { return false; } }
template<typename T> bool setmaxeq(T & a, T b) { if(b >= a) { a = b; return true; } else { return false; } }
template<typename T> T gcd(T a, T b) { return (b == 0 ? a : gcd(b, a % b)); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

// ---- ----

int n, c[11];
double P[102][102][102];
double E[102][102][102]; 

int main() {
	cin >> n;
	inc(i, n) {
		int a;
		cin >> a;
		inc(j, a) { c[j]++; }
	}
	
	P[c[0]][c[1]][c[2]] = 1;
	E[c[0]][c[1]][c[2]] = 0;
	incII(i, c[0], n) {
	incII(j, c[1], n) {
	incII(k, c[2], n) {
		vector<int> v = { n, i, j, k };
		if(! is_sorted(RALL(v))) { continue; }
		
		double x = n - i;
		double y = i - j;
		double z = j - k;
		double s = x + y + z;
		double PP = P[i][j][k];
		double EE = E[i][j][k] + PP * n / s;
		
		P[i + 1][j][k] += PP * x / s;
		P[i][j + 1][k] += PP * y / s;
		P[i][j][k + 1] += PP * z / s;
		
		E[i + 1][j][k] += EE * x / s;
		E[i][j + 1][k] += EE * y / s;
		E[i][j][k + 1] += EE * z / s;
	}
	}
	}
	
	printf("%.12f\n", E[n][n][n]);
	
	return 0;
}