A, B = map(int, input().split())

if A <= 2 * B:
    print('0')
else:
    print(A - 2 * B) A, B = map(int, input().split()) A map(int, input().split()) map int input().split() ().split () input split B if A <= 2 * B:
    print('0')
else:
    print(A - 2 * B) A <= 2 * B A 2 * B 2 B print('0') print '0' print(A - 2 * B) print A - 2 * B A 2 * B 2 B B = map(int, input().split()) map(int, input().split()) B A, B = map(int, input().split()) map(int, input().split()) A
A, B = map(int, input().split())

if A <= 2 * B:
    print('0')
else:
    print(A - 2 * B)