Problem:
Pair of Primes

We arrange the numbers between 1 and N (1 <= N <= 10000) in increasing
order and decreasing order like this:

1 2 3 4 5 6 7 8 9 . . . N
N . . . 9 8 7 6 5 4 3 2 1

Two numbers faced each other form a pair. Your task is to compute the number of pairs P such that both
numbers in the pairs are prime.

Input

Input contains several test cases. Each test case consists of an integer N in
one line.

Output

For each line of input, output P .

Sample Input

1
4
7
51

Output for the Sample Input

0
2
2
6

Solution in JAVA (judge verdict: Accepted)

import java.util.Scanner;

public class Main {

	static Scanner sc = new Scanner(System.in);
	static boolean[] isPrime = new boolean[10001];

	public static void main(String[] args) {
		for (int i = 2; i <= 10000; ++i) {
			isPrime[i] = isPrime(i);
		}
		while (sc.hasNext()) {
			int N = sc.nextInt();
			int ans = 0;
			for (int i = 1; i <= N; ++i) {
				if (isPrime[i] && isPrime[N - i + 1]) ++ans;
			}
			System.out.println(ans);
		}
	}

	static boolean isPrime(int v) {
		for (int i = 2; i * i <= v; ++i) {
			if (v % i == 0) return false;
		}
		return true;
	}
}