C++ :

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
using namespace std;
int main(){
	int w,n,a[100000];
	cin>>w>>n;
	for(int i=1;i<=n;i++)
		cin>>a[i];
	sort(a+1,a+n+1);
	int i=1,j=n,ans=0;
	while(i<=j){
		if(a[i]+a[j]<=w){
			ans++;
			i++;
			j--;
		}
		if(a[i]+a[j]>w){
			ans++;
			j--;
		}
	}
	cout<<ans;
	return 0;
}

Pascal :

var
  i,j,k,m,n,ans:longint;
  a:array[0..30001]of longint;
procedure   qsort(l,r:longint);
  var
    i0,j0,mid,e:longint;
  begin
    i0:=l;j0:=r;
    mid:=a[(i0+j0)div 2];
    repeat
      while a[i0]>mid do i0:=i0+1;
      while a[j0]<mid do j0:=j0-1;
      if i0<=j0 then begin e:=a[i0];a[i0]:=a[j0];
      a[j0]:=e;i0:=i0+1;j0:=j0-1;
      end;
    until i0>j0;
    if l<j0 then qsort(l,j0);
    if i0<r then qsort(i0,r);
  end;
begin
   readln(k);
  readln(n);
  for i:=1 to n do readln(a[i]);

  qsort(1,n);
  i:=1;j:=n;ans:=0;
  while i<=j do
      if (i<j)and ( a[i]+a[j]<=k) then
      begin ans:=ans+1;i:=i+1;j:=j-1;end
        else
          begin
          ans:=ans+1;
          i:=i+1;
          end;



  write(ans);
end.