# coding: utf-8
# Your code here!
def func(num):
    return num**2-a*num-b*num+a*b

a,b=map(int,input().split())

dt=10**-4

al=(b-a)*10**4

ans=0
for i in range(al-1):
    high=(i+1)*10**-4+a
    low=i*10**-4+a
    #print(high)
    ans+=-(func(high)+func(low))/2*dt

print(ans)