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 {

	public static void main(String[] args) {

		boolean[] pmap = new boolean[10001];
		pmap[1]=true;
		for(int i=2;i<10000;i++)
			if(!pmap[i])
				for(int j=2;i*j<=10000;j++)
					pmap[i*j]=true; //素数でない


		Scanner scan = new Scanner(System.in);

		while(scan.hasNext()){
			int n = scan.nextInt();

			int c=0;
			for(int i=1;i<=n;i++){
				int j=n+1-i;
				if(!pmap[i] && !pmap[j])
					c++;
			}
			System.out.println(c);
		}
	}

}