N,M=map(int,input().split())
if N%2==0 and M%2==0:
    print(0)
    exit()
if N%4==0:
  print(N//4)
  exit()
if M%4==0:
  print(M//4)
  exit()
if N%2==0:
  print(M//4)
  exit()
elif M%2==0:
  print(N//4)
  exit()
else:
  print(N//4+M//4)