#32960: 布林值寫法
imlindora@gmail.com
(Augus)
a0,b0=map(int,input().split())
c=0
a=a0%2==0
b=b0%2==0
if (a==True and b==True) or (a==False and b==True) or (a==True and b==False):
print((b0-a0)//2+1)
else:
print((b0-a0)//2)