# coding: utf-8
# Your code here!

a,b =list(map(int,input().split()))
if(a-2*b>0):
    print(a-2*b)
else:print("0") a,b =list(map(int,input().split())) a list(map(int,input().split())) list map(int,input().split()) map int input().split() ().split () input split b if(a-2*b>0):
    print(a-2*b)
else:print("0") a-2*b>0 a-2*b a 2*b 2 b 0 print(a-2*b) print a-2*b a 2*b 2 b b =list(map(int,input().split())) list(map(int,input().split())) b a,b =list(map(int,input().split())) list(map(int,input().split())) a
# coding: utf-8
# Your code here!

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