#! /usr/bin/python
"""Usage: colsum.py column-number [input-files ...]
"""
import fileinput, string, sys

def die(reason, file=None, line=None):
	if file:
		fileline = "file %s line %d: " % (file, line)
	else:
		fileline = ""
	sys.stderr.write(fileline + reason + '\n')
	sys.exit(1)

total = 0

try:
	colnum = int( sys.argv.pop(1) ) - 1
except IndexError:
	die(__doc__)

for lin in fileinput.input():
	items = string.split(lin)
	file, linno = fileinput.filename(), fileinput.filelineno()
	try:
		field = items[colnum]
		number = int(field)
		total = total + number
	except IndexError:
		die("not enough fields", file, linno)
	except ValueError:
		die("unable to parse number %s" % `field`, file, linno)

print total