N = input()
A = [0] * 11
for i in range(N):
    for x in map(int, raw_input().strip().split(" ")):
        A[x] += 1
ans = 0
for i in range(11):
    if A[i] >= 2:
        ans += A[i] / 2
        A[i] %= 2
print(ans + sum(A) / 4)