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 C (judge verdict: Accepted)

#include <stdio.h>
int is_prime(int n){
  int i;
  if(n==1)
    return 0;
  for(i=2;i*i<=n;i++)
    if(n%i==0)
      return 0;
  return 1;
}
int main(void){
  int n,c,i;
  while(scanf("%d",&n)!=EOF){
    c=0;
    for(i=1;i<=n;i++){
      if(is_prime(i)&&is_prime(n-i+1))
	c++;
    }
    printf("%d\n",c);
  }
  return 0;
}