N = int(input())
A = list(map(int, input().split()))

from itertools import groupby
import bisect

ans = 0
A.sort()
for k, g in groupby(A):
    n = len(list(g))
    if n < 2:
        continue
    s = n * (n-1) // 2
    t = bisect.bisect_right(A, 2*k-1) - n
    ans += s * t

print(ans)