val numbers = arrayOf(2, 3, 5, 7, 11, 13, 17, 19)
var str = ""
for (i in numbers.indices) {
if (i%2 == 1) {
continue
}
if (str.isNotEmpty()) {
str += "-"
}
str += numbers[i]
}
//str is "2-5-11-17"
println("str is $str")