n = int(input())
A = list(map(int,input().split()))
ans = 0
act = 0
i = 0
j = 0

while i < len(A):
  act = A[i]
  j = i + 1
  while j < len(A):
    if A[j] == act:
      ans += 1
      A.pop(j)
      A.pop(i)
      break
    j += 1
  else:
    i += 1

print(ans)