import threading
x = 0
l = []
def foo():
 global l
 global x
 for i in range(1000):
     x += 1
     l=l+[x]
def bar():
 global l
 global x
 for i in range(1000):
     x -= 1
     l=l+[x]
t1 = threading.Thread(target=foo)
t2 = threading.Thread(target=bar)
t1.start()
t2.start()
t1.join()
t2.join() # Wait for completion
print x
#print l