import java.util.*

fun main(args: Array<String>) {
    val count = readLine()!!.toInt()
    val items = Array<Int>(10, {0})
    (1..count).forEach {
        readLine()!!.split(" ").map { items[it.toInt()]++ }
    }
    val ans = items.map { it / 2 }.sum() + items.map { it % 2 }.sum() / 4
    println(ans)
}