list1=[]
for i in range(100):
    list1.append(i)
    
AB=input()
AB=AB.rstrip().split(" ")
A=int(AB[0])
B=int(AB[1])

if (A+B)%3==0:
    count=0
    for j in range(A,B+1):
        if j%3==0:
            count=count+1
elif (A+B)%3==1:
    count=0
    for j in range(A,B+1):
        if j%3==2:
            count=count+1
elif (A+B)%3==2:
    count=0
    for j in range(A,B+1):
        if j%3==1:   
            count=count+1
print(count)