import kotlin.math.*

fun main()
{
    val N = readLine()!!.toInt()
    val cnt = Array<Int>(11, {0})

    repeat(N) {
        readLine()!!.split(" ").map(String::toInt).forEach { cnt[it]++ }
    }

    var ans = 0
    var sum = 0
    var pairs = 0
    cnt.forEach { c ->  sum += c; pairs += c / 2 }
    ans = pairs + (sum - pairs * 2) / 4
    println(ans)
}