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