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

if a <= b or a - (b * 2) <= 0:
    print("0")

else:
    print(a - (b * 2)) a,b = map(int,input().split()) a map(int,input().split()) map int input().split() ().split () input split b if a <= b or a - (b * 2) <= 0:
    print("0")

else:
    print(a - (b * 2)) a <= b or a - (b * 2) <= 0 a <= b a b a - (b * 2) <= 0 a - (b * 2) a b * 2 b 2 0 print("0") print "0" print(a - (b * 2)) print a - (b * 2) a b * 2 b 2 a,b = map(int,input().split()) map(int,input().split()) a b = map(int,input().split()) map(int,input().split()) b
a,b = map(int,input().split())

if a <= b or a - (b * 2) <= 0:
    print("0")

else:
    print(a - (b * 2))
