a, b = map(int, input().split())
while(a<0 or b<0 or a>10**10 or b>10**10  ):
    a, b = map(int, input().split())

if (a==0 or b==0):
        ma=0
        print(ma)
elif (a+b<3):
    ma=0
    print(ma)
elif (a+b>=3) :
    ma=(a+b) // 3
    print(ma)