Goldbach Pair

/*
 * Problem : Write an even number as the sum of two primes.
 * Input   : An even integer n >= 4.
 * Output  : Two primes p q with p <= q.
 * Approach: Try the smallest prime first.
 * Time    : O(n sqrt n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
        // This helper returns true if the number is prime.
        static boolean isPrime(long x) {
            if (x < 2) {
                return false;
            }
            for (long d = 2; d * d <= x; d++) {
                if (x % d == 0) {
                    return false;
                }
            }
            return true;
        }

    // This method solves the task. It receives the input and returns the answer.
    static String[] solve(long n) {
        // Step 1: Try every p from 2 up to n / 2. The smaller number is never bigger than n / 2.
        for (long p = 2; p <= n / 2; p++) {
            // Step 2: Both p and n - p must be prime.
            if (isPrime(p) && isPrime(n - p)) {
                return new String[] {p + " " + (n - p)};
            }
        }
        return new String[] {"none"};
    }

    public static void main(String[] args) {
        long n = new Scanner(System.in).nextLong();
        System.out.println(String.join("\n", solve(n)));
    }
}