#!/usr/bin/python
# -*- coding: utf-8 -*-

N = int(raw_input())
tmp,arys = [],[]
ans = 0

for i in xrange(N):
       	ini = map(int, raw_input().split())
       	tmp.extend(ini)
tmp.sort()

for i in xrange(1,11):
       	arys.append(tmp.count(i))
arys.sort(reverse=True)

for (i,val) in enumerate(arys):
       	print i , val
       	ans += val / 2
       	if val % 2 == 1:
       		val = 1
       	else:
       		val = 0

print ans + arys.count(1) / 4