from math import factorial
from decimal import *

getcontext().prec = 100

def C(n, k):
    return Decimal(factorial(n)) / Decimal((factorial(n-k) * factorial(k)))

H = map(Decimal, range(1025))
d_3 = Decimal(3)
d_1 = Decimal(1.0)
c = C(n, 1025)

def tp(n):
    m = Decimal(1)
    for i in H:
        m *= (n/d_3 - i) * d_1 / (n-i) * (n-((n/d_3)-i)) / (n-i)
    return n

all = sum([tp(n) * c for n in map(Decimal, xrange(1025, 2500))])

print 1 - all