1 2 3 4 5 6 7 8 9 10 11 12
a = int(input()) b = int(input()) e1 = 0 e2 = 0 if a%2==0 and b%2==1: print (-(b-a+1)//2) if a%2==1 and b%2==0: print ((b-a+1)//2) if a%2==1 and b%2==1: print ((b-a)//2-b) if a%2==0 and b%2==0: print (-(b-a)//2+b)