#!/usr/bin/env python

import os
import sys


# loads 2D gnuplot data file as command line argument
# 2D gnuplot data file format:
# x y f(x,y) } n-times    \
#            } empty line | m-times
# x y f(x,y) } n-times    /
# extracts the values of x corresponding to y == 0.0
# prints result to STDOUT
def main():
    if len(sys.argv) <= 1:
        print "Usage: %s <file name>" % sys.argv[0]
        return 1
    filename = sys.argv[1]
    if not os.path.exists(filename):
        print "Error: can't find file %s" % filename
        return 2

    f = open(filename, 'r')
    while True:
        line = f.readline()
        if not len(line):
            break
        if line == '\n':
            continue
        items = line.split()
        try:
            if float(items[1]) == 0.0:
                print line[:-1]
        except:
            print "Error: unknown file format"
            return 3
    return 0

if __name__ == "__main__":
    sys.exit(main())