import bisect
import collections

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

A.sort()
ans = 0
for l, n in collections.Counter(A).items():
    if n >= 2:
        m = bisect.bisect(A, l*2-1) - n
        ans += m * n * (n-1) // 2
print(ans)