package main

import . "fmt"
import . "os"
import bf "bufio"
import . "slices"

func main() {
	rd:=bf.NewReader(Stdin)
	var n int
	Fscan(rd,&n)
	a:=make([]int64,2*n)
	for i:=range a {
		Fscan(rd,&a[i])
	}
	Sort(a)
	s:=int64(0)
	for k:=0;k<n;k++ {
		s+=a[2*k]*a[2*k+1]
	}
	Println(s)
}