#fileencoding: utf-8
from __future__ import print_function

def main():
    N = int(raw_input())
    items = sorted([j for i in range(N) for j in list(map(int, raw_input().strip().split(" ")))])
    bucket = {}
    for i in items:
        bucket[i] = bucket.get(i, 0) + 1
    power = 0
    amari = 0
    for v in bucket.values():
        power += v // 2
        amari += (v - (v//2) * 2)
        power += (amari//4)
        amari -= (amari//4) * 4
    print(power)

if __name__ == "__main__":
    main()