#!/usr/bin/env python

import sys,string

count = 0
sum = 0.0

ignore=0

def usage(retval):
	sys.stderr.write('Usage: %s [-i]\n' % sys.argv[0])
	sys.stderr.write('-i says to ignore lines that cannot be converted to a floating point number - IE, do not error out\n')
	sys.exit(retval)

while sys.argv[1:]:
	if sys.argv[1] == '-i':
		ignore=1
		del sys.argv[1]
	elif sys.argv[1] == '-h':
		del sys.argv[1]
		usage(0)
	else:
		usage(1)

while 1:
	line = sys.stdin.readline()
	if not line:
		break
	try:
		t = string.atof(string.strip(line))
	except:
		sys.stderr.write('Could not convert %s to a float\n' % string.strip(line))
		if not ignore:
			sys.exit(1)
	else:
		count = count + 1
		sum = sum + t

if count == 0:
	print 0
else:
	print sum/count