tracks/kotlin/exercises/nth-prime/.meta/src/reference/kotlin/Prime.kt in trackler-2.2.1.62 vs tracks/kotlin/exercises/nth-prime/.meta/src/reference/kotlin/Prime.kt in trackler-2.2.1.63

@@ -1,10 +1,15 @@
 import java.math.BigInteger
 
 object Prime {
 
-    fun nth(n: Int): Int = primes().drop(n - 1).first().toInt()
+    fun nth(n: Int): Int {
+        require(n > 0) { "There is no zeroth prime." }
 
-    fun primes(): Sequence<BigInteger> = generateSequence(BigInteger.valueOf(2)) { previous ->
+        return primes().drop(n - 1).first().toInt()
+    }
+
+    private fun primes(): Sequence<BigInteger> = generateSequence(BigInteger.valueOf(2)) { previous ->
         previous.nextProbablePrime()
     }
+
 }