def main():
    d = {}
    ans = 0
    N = int(input())
    for i in range(N):
        l = map(int, input().split())
        for e in l:
            d[e] = d.get(e, 0) + 1

    #print(d)

    for k, v in d.items():
        tmp = v
        while tmp >= 2:
            tmp = tmp - 2
            d[k] = d[k] - 2
            ans += 1

    #print(d)
    #print(ans)

    sum_values = 0
    for k, v in d.items():
        sum_values += v

    ans = ans + sum_values // 5

    print(ans)

if __name__ == '__main__':
    main()