fun fib(n: Int): Int {
require(n >= 0)
fun fib(k: Int, a: Int, b: Int): Int =
if (k == 0) a else fib(k - 1, b, a + b)
return fib(n, 0, 1)
}
fun main(args: Array<String>) {
for (i in 0..20) print("${fib(i)} ")
println()