C++ :

#include<iostream>
#include<cstdlib>
#include<algorithm>
using namespace std;
int main()
{
	int w,n,a[30001],number=0,sheng=0;
	cin>>w>>n;
	for(int i=1;i<=n;++i)
	  cin>>a[i];
	sort(a+1,a+n+1);
	int s=0,h=n+1;
	while(1)
     {
		s++;
		h--;
		if(a[s]+a[h]<=w)
		  number++;
		if(a[s]+a[h]>w)
         {
			--s;
			number++;
         }
         if(s==h)
		   break;
		 if(s>h)
          {
				number--;
				break;
          }
     }
     cout<<number;
	 //system("pause");
	 return 0;
}

Pascal :

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

Java :

import java.util.Arrays;
import java.util.Scanner;

public class Main {
	
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int max = in.nextInt();
		int n = in.nextInt(), count = 0, l = 0, r = n-1;
		int[] number = new int[n];
		for ( int i = 0; i < number.length; i++ ) number[i] = in.nextInt();
		Arrays.sort(number);
		while ( l <= r ) {
			if ( number[l] + number[r] <= max ) l++;
			r--;
			count++;
		}
		System.out.println(count);
	}
	
}