#yuki352
import math

n=int(raw_input())
ls=[]
for i in xrange(n+1):
 ls.append(math.factorial(i))
res=2.0
for i in xrange(3,n+1):
 res+=2.0/i
 for j in xrange(1,i-1):
  for k in xrange(1,i):
   for l in xrange(k+1,i):
    res+=2.0*k*l*ls[i-3]/ls[i-1]/i
print res