import math
import sys
n=int(input())
s=list(map(int,input().split()))
x=int(input())
b=list()
for item in s:
    for iitem in s:
        b.append(item+iitem)
if x in b:
    print(b.count(x)//2)

/**************************************************************
	Problem: 1766
	User: admin
	Language: Python
	Result: Accepted
	Time:47 ms
	Memory:34480 kb
****************************************************************/