Wrong with this script?

[R.Meijer]

Hi, I've been busy with an experimental script, and I can't seem to
see what is wrong with it, can somebody tell me?

Here it is:

a = 0
b = 1
mainloop = 1

print "Welcome to pyFibo"
print "For more information type \'help\'"
while mainloop==1:
      limit = input("Until what number do you want to see the
Fibonacci series?")
      if limit=="help":
          print "The Fibonacci series is a worldfamous series of
numbers.\
Each consecutive number is calculated by adding the previous two
numbers to\
each other."
      else:
          while b < limit:
                print b
                a, b = b, a+b
          print "Want to do another series?"
          again = input("(Type yes for another series, or anything
else to quit.)"
          if again!="yes":
          mainloop = 0



Any help is appreciated, thanks ^_^