C++ :

#include<iostream>
#include<algorithm>
using namespace std;
int a[30005];
int main(){
	int w,n;
	cin>>w>>n;
	for (int i=0;i<n;i++)
		cin>>a[i];
	sort(a,a+n);
	int i,j,ans=0;
	for (i=0,j=n-1;i<j;){
		if (a[i]+a[j]>w)
			ans++,j--;
		else ans++,i++,j--;
	}
	if (i==j) ans++;
	cout<<ans<<endl;
	return 0;
}

Pascal :

var i,j,t,n,w,s,x,y:longint;p:array[1..30000]of longint; 
    a:array[1..30000]of boolean; 
procedure qsort(l,r:longint); 
var mid,i,j:longint; 
begin
  mid:=p[(l+r) div 2]; 
  i:=l;j:=r; 
  repeat
    while p[i]<mid do inc(i); 
    while p[j]>mid do dec(j); 
    if i<=j then begin t:=p[i];p[i]:=p[j];p[j]:=t;i:=i+1;j:=j-1;end; 
  until i>j; 
  if l<j then qsort(l,j); 
  if i<r then qsort(i,r); 
end; 
begin
  readln(w); 
  readln(n); 
  for i:=1 to n do readln(p[i]); 
  fillchar(a,sizeof(a),true); 
  qsort(1,n); 
  s:=0;x:=w;y:=0; 
  for i:=n downto 1 do
    begin
      if a[i]=false then continue; 
      x:=x-p[i]; 
      y:=y+1; 
      a[i]:=false; 
      j:=1; 
      repeat
        if a[j] and(p[j]<=x) then begin x:=x-p[j];a[j]:=false;end; 
        j:=j+1; 
        y:=y+1; 
      until (y=2)or(j=n)or(p[j]>x)or(x=0); 
      s:=s+1; 
      x:=w; 
    end; 
  writeln(s); 
end.