C++ :

#include<bits/stdc++.h>
using namespace std;
int main(){
	long long n,a[10005],s=0,x=2,z=0;
	cin>>n;
	for(int i=0;i<n;i++) cin>>a[i];
	sort(a,a+n);
	for(int i=0;i<=n-1;i+=2) cout<<a[i]<<" ";
	for(int i=n-2;i>=0;i-=2) cout<<a[i]<<" ";
	return 0;
}

Pascal :

var n,i,j,x,t:longint;a,f:array[1..1000]of longint;
begin
  read(n);
  for i:=1 to n do read(a[i]);
  for i:=1 to n-1 do
    for j:=i+1 to n do
      if a[i]<a[j] then begin t:=a[i];a[i]:=a[j];a[j]:=t;end;
  x:=n div 2+1;
  f[x]:=a[1];
  for i:=2 to n do
      if i mod 2=1 then
        begin
          f[x-i+1]:=a[i];
          x:=x-i+1;
        end
      else
        begin
          f[x+i-1]:=a[i];
          x:=x+i-1;
        end;
  for i:=1 to n-1 do write(f[i],' ');
  writeln(f[n]);
end.