from random import randint
A = [randint(1, 1000) for j in range(100)]
count = 0
for i in range(len(A)):
    for j in range(i + 8, len(A)):
        if (A[i] - A[j]) % 999 == 0 or (A[j] - A[i]) & 999 == 0:
            count += 1
print(count)