# https://yukicoder.me/problems/no/29 n = int(input()) A = [0]*10 for _ in range(n): tmp = list(map(int, input().split())) for t in tmp: A[t-1] += 1 ans = 0 for i in range(10): ans += A[i]//2 A[i] = A[i] % 2 ans += sum(A)//4 print(ans)