schensted.dat problem for sctf 2016

schensted.dat

#!/usr/bin/env python

#Open file and read file
f = open('schensted.dat')
numbers = f.read()

checked = 0
unchecked = 1
current =  str(numbers[0])
longest = ""

#Loop until we reach the second last character (last is \n")
while unchecked < (len(numbers)-1):
 
  #Check if unchecked is greater than the current number
  if int(numbers[checked]) <= int(numbers[unchecked]):
   
    #if it is append the current number to our string and increase vars
    current = str(current) + str(numbers[checked])
    current = str(current)
    unchecked = unchecked + 1
    checked = checked + 1
  
  else:
    current = str(current) + str(numbers[checked])
    #If it is not reset current and if current is greater than longest set longest
    if len(str(current)) > len(str(longest)):
      longest = current
    unchecked = unchecked + 1
    checked = checked + 1
    current = ""
print(longest)