Problem A - Goldbach's Conjecture
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Goldbach's Conjecture: For any even number n greater than or equal to 4,
there exists at least one pair of prime numbers p1 and p2 such that n =
p1 + p2.

This conjecture has not been proved nor refuted yet. No one is sure
whether this conjecture actually holds. However, one can find such a
pair of prime numbers, if any, for a given even number. The problem here
is to write a program that reports the number of all the pairs of prime
numbers satisfying the condition in the conjecture for a given even
number.

A sequence of even numbers is given as input. Corresponding to each
number, the program should output the number of pairs mentioned above.
Notice that we are interested in the number of essentially different
pairs and therefore you should not count (p1, p2) and (p2, p1)
separately as two different pairs. However, a pair where p1 = p2 does
count. Also, 1 is not a prime number for the purposes of this problem.

Input 
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An integer is given in each input line. You may assume that each integer
is even, and is greater than or equal to 4 and less than 2^15. The end
of the input is indicated by a number 0, that should not be processed.

Output 
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Each output line should contain an integer number. No other characters
should appear in the output.

Sample Input 
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6
10
12
0

Output for Sample Input
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1
2
1