function solve(arr) {
    //get the date from input and format it to fit the ISO standart
    var formattedDateFromInput = arr[0].split('-').reverse().join('-');
    var startDate = new Date(formattedDateFromInput);
    var x = 1000;
    var yStarrt = startDate ? startDate.getUTCFullYear() : startDate.getFullYear();
///WHY THIS CONDITION WORKS????
    if (yStarrt < 2000) {x = 999;};
    var endDate = addDays(startDate, x);
   endDate = endDate.toISOString()
     .replace(/T.*/, '').split('-').reverse().join('-');
    console.log(endDate);
//function to add days to a given date.
	function addDays(startDate,numberOfDays)
	{
		var returnDate = new Date(
								startDate.getFullYear(),
								startDate.getMonth(),
								startDate.getDate()+numberOfDays,
								startDate.getHours(),
								startDate.getMinutes(),
								startDate.getSeconds());
		return returnDate;
	}
}