import java.io.PrintWriter
import java.util.*

fun PrintWriter.solve() {
    val n = nextInt()
    val a = Array(2 * n) { nextLong() }
    a.sort()
    println((0 until n).map { a[2 * it] * a[2 * it + 1] }.sum())
}

fun main() {
    val writer = PrintWriter(System.out, false)
    writer.solve()
    writer.flush()
}

// region Scanner
private var st = StringTokenizer("")
private val br = System.`in`.bufferedReader()

fun next(): String {
    while (!st.hasMoreTokens()) st = StringTokenizer(br.readLine())
    return st.nextToken()
}

fun nextInt() = next().toInt()
fun nextLong() = next().toLong()
fun nextLine() = br.readLine()
fun nextDouble() = next().toDouble()
// endregion