import threading

n=0
nVegades=1000000
critic=threading.Lock()

def fil1():
    global n
    for i in range(nVegades):
        critic.acquire()
        n = n + 1
        critic.release()

def fil2():
    global n
    for i in range(nVegades):
        critic.acquire()
        n = n - 1
        critic.release()

def principal():
    t1= threading.Thread(target=fil1)
    t2= threading.Thread(target=fil2)
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    print(n)

if __name__=="__main__":
    principal()