n = int(input())


B = []

for i in range(n):
    B += list(map(lambda x: int(x) % 10, input().split()))

A = [B.count(i) for i in range(10)]
ans = 0
for i in range(10):
    ans += A[i] // 2
    A[i] = A[i] % 2

ans += sum(A) // 4

print(ans)