#!/usr/bin/env python3

from fractions import Fraction

def cut(state, i):
    return state[:i] + (state[i]-1,) + \
           tuple(n + 1 for n in state[i+1:])

def search(state=(1, 0, 0, 0, 0), cache={}):
    if state in cache:
        return cache[state]
    if sum(state) == state[-1] == 1:
        return 1
    r = 0
    for i, p in enumerate(state):
        if not p:
            continue
        r += Fraction(p, sum(state)) * \
             search(cut(state, i), cache)
    r += (sum(state) == 1)
    cache[state] = r
    return r

print(float(round(search(), 6) - 2))