n = int(input())
num_set = []
for i in range(n):
    inp = input().split()
    num_set += inp
    
count = 0
rem = 0
for i in range(1,11):
    n = num_set.count(str(i))
    count += int(n/2)
    rem += n%2
    
print(count + int(rem/4))