from collections import defaultdict
from bisect import bisect_left, bisect_right
from math import comb

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

D = defaultdict(int)
for a in A:
    D[a] += 1

ans = 0
for n, c in D.items():
    if c == 1:
        continue
    a = comb(c, 2)
    b = bisect_left(A, 2*n)-c
    ans += a*b

print(ans)