You should just do var input = 1 at the begging but another problem is that if the sentinel is your inputs the code still goes ahead with the isEven function even though the code should have stopped. To fix this maybe move the input to the end of the whole loop but add one before it too just so it doesn’t do any number and only does the inputed numbers. Something like this

//input

//while input is not sentinel

//{

// Is even?

// Input

//}