What Is the Sentinel Value in the Following Code Snippet

What is the sentinel value in the following code snippet?
Public static void main(String[] args)
{
Int age = 0;
Int sumOfAges = 0;
Int stop = 1;
Scanner reader = new Scanner(System.in) ;
System.out.println("Enter an age (-1 to stop) : ") ;
Age = reader.nextInt() ;
While (age != -1)
{
SumOfAges = sumOfAges + age;
System.out.println("Enter an age (-1 to stop) : ") ;
Age = reader.nextInt() ;
}
System.out.println("Sum of ages " + sumOfAges) ;
Return 0;
}

A) 0
B) 1
C) 2
D) -1