Consider an array of n positive integers a1, a2, ..., an, having values between 1 and 106 and an integer x. Write a program to determine the number of pairs (ai, aj), where 1 ≤ i < j ≤ n and ai + aj = x.

Input

The first line contains the integer n (1 ≤ n ≤ 105). The second line contains n integers - the elements of array that can be repeated. On the third line the integer x (1 ≤ x ≤ 2 * 106) is given.

Output

Print the calculated number of pairs.