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