import sys
input = lambda : sys.stdin.readline().rstrip()
sys.setrecursionlimit(max(1000, 10**9))
write = lambda x: sys.stdout.write(x+"\n")


# inputna
n,m = list(map(int, input().split()))
if n%2==0 and m%2==0:
    ans = 0
elif n%2==0:
    ans = n//4
elif m%2==0:
    ans = m//4
else:
    ans = n//4 + m//4
print(ans)