# numbtree3.py
# Written by Todd Wareham for CS 2500
#  using code supplied by Jason Gedge
"""
Given an integer n as a command-line argument, computes and prints the 
 number of unrooted binary trees with n leaves.

This version is implemented using speciial-purpose number formatting code.
"""

import sys

if (len(sys.argv) != 2):
    print "usage:", sys.argv[0], "n"
    sys.exit(1)

numBT = 1
for i in range(3, int(sys.argv[1]) + 1, 1):
    numBT *= ((2 * i) - 5)

sigDigits = 8

sval = str(abs(numBT))
exp = len(sval) - 1

if (len(sval) < (sigDigits + 2)):
    sig = sval[1:]
else:
    sig = str(round(float(sval[1:sigDigits + 1] + "." + sval[sigDigits + 1])))
ret = sval[0] + "." + sig
print ret + "e+" + str(exp)