#21308: python 3


jerjer920813@gmail.com (YJ)


s = list(map(int,input().split()))
a = []
if s[0] > s[1]:
s[0],s[1] = s[1],s[0]
for i in range(s[0],s[1]+1):
if i % 2 == 0:
a.append(i)
print(sum(a))