C++ :

#include<iostream>
#include<algorithm>
using namespace std;
int a[30001],w,n,s,i,j; 
main()
{
  cin>>w>>n;
  for(i=0;i<n;i++)
    cin>>a[i];
  sort(a,a+n);
  i=0;j=n-1;
  while(i<=j)
  {
    if(a[i]+a[j]<=w)i++; 
    s++;j--;                
  }
  cout<<s;
  return 0;     
}

Pascal :

var    a:array[1..100000] of longint;
  i,j,w,n,x:longint;
procedure qsort(l,r:longint);
var i,j,m,p:longint;
begin
  i:=l; j:=r; m:=a[(l+r) div 2];
  repeat
    while a[i]<m do inc(i);
    while a[j]>m do dec(j);
    if i<=j then
    begin p:=a[i]; a[i]:=a[j]; a[j]:=p; inc(i); dec(j); end;
  until i>j;
  if i<r then qsort(i,r);
  if l<j then qsort(l,j);
end;begin
  readln(w); readln(n);
  for i:=1 to n do readln(a[i]);
  qsort(1,n);
  i:=1; j:=n; x:=0;
  repeat
    if i=j then begin inc(x); break; end;
    if a[j]+a[i]<=w then begin inc(i); dec(j); inc(x); end
    else begin dec(j); inc(x); end;
  until i>j;
  writeln(x);
end.