import java.util.*;

public class Main {
    public static void main(String[] args) {
        int offset=0;

        Scanner sc=new Scanner(System.in);
        int len=sc.nextInt();
        int[] arr=new int[len];
        int[] result=new int[len];
        for(int i=0;i<len;i++){
            arr[i]=sc.nextInt();
        }
        /*
        int a=0;
        while(a<len){
            Value min=findMin(arr);
            result[offset++]=min.a;
            result[offset++]=min.b;
            arr[min.offsetA]=0;
            arr[min.offsetB]=0;
            a+=2;
        }
        StringBuilder builder=new StringBuilder(len*4);
        for(Integer c:result){
            builder.append(c).append(" ");
        }
        System.out.println(builder.toString().replaceFirst(" $",""));
         */
    }
    private static Value findMin(int[] arr){
        int minA=Integer.MAX_VALUE;
        int minB=Integer.MAX_VALUE;

        int offsetA=-1;
        int offsetB=-1;


        int firstIndex=Math.max(skipZeros(arr),1);

        int prevOffset=firstIndex-1;
        int prev=arr[prevOffset];

        for(int i=firstIndex;i<arr.length;i++){
            int v=arr[i];
            if(v==0) continue;

            if(minA<prev){
                prevOffset=i;
                prev=v;
                continue;
            }
            offsetA=prevOffset;
            offsetB=i;

            minA=prev;
            minB=v;

            prevOffset=i;
            prev=v;
        }
        return new Value(minA,minB,offsetA,offsetB);
    }
    private static int skipZeros(int[] arr){
        for(int i=0;i<arr.length;i++){
            if(arr[i]!=0){
                return i;
            }
        }
        return -1;
    }
    private record Value(Integer a, Integer b, int offsetA,int offsetB){}
}