import sys
input = sys.stdin.readline

n = int(input())
a = list(map(int, input().split()))

a.sort()
ans = 0
for i in range(2,n):
    l = 0
    r = i - 1
    while l < r:
        if a[l] + a[r] > a[i]:
            ans += (r-l)
            r -= 1
        else:
            l += 1
print(ans)