#! /usr/bin/env python

import sys

import os

if len(sys.argv)>1 and sys.argv[1] in ["-h","--help"]:

    print """

This utility just prints the length of the longest path

in the revision graph from revison 0 to the current one.

"""

    exit(0)

plist = os.popen("hg parents --template='{rev}\n'").readlines()

if len(plist)>1:

    print "You are in the process of merging"

    exit(1)

PAR = int(plist[0])

f = os.popen("hg log -r 0:tip --template='{rev} {parents}\n'").readlines()

REV = -1

lengths=[]

for l in f:

    REV+=1

    s = l.split()

    rev = int(s[0])

    if REV != rev:

        print "Something is seriously wrong"

        exit(1)

    if len(s) == 1:

        par1 = par2 = rev - 1

    elif len(s) == 2:

        par1 = par2 = int(s[1].split(":")[0])

    else:

        par1 = int(s[1].split(":")[0])

        par2 = int(s[2].split(":")[0])

    if rev == 0:

        lengths.append(0)

    else:

        lengths.append(max(lengths[par1],lengths[par2])+1)

print lengths[PAR]