class AccountB
{
 private int amount;

 public AccountB()
 {
  amount = 0;
 }

 public AccountB(int sum)
 {
  amount=sum;
 }

 public void deposit(int sum)
 {
  amount+=sum;
 }

 public void withdraw(int sum) throws AccountException
 {
  if(sum<=amount)
      amount-=sum;
  else
     throw new AccountException("overdraw");
 }

 public int balance()
 {
  return amount;
 }
}