n = int(input())

nums = [int(i) for i in input().split(' ')]

nums.sort()

x=0

for i in range(n-2):

for j in range(i+1,n-1):
    k=j+1
    while k<n:
        if nums[i]+nums[j]>nums[k]:
            x+=1
        else:
            break
        k = k + 1

print(x)

#技术有限,只能爆破了