import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

N,*A = map(int,read().split())

counter = [0] * (101)
for x in A:
    counter[x] += 1

answer = 0
rest = 0
for x in counter:
    q,r = divmod(x,2)
    answer += q
    rest += r

answer += rest // 4
print(answer)