C :

#include<stdio.h>
#include<stdlib.h>
int a[30001];
int ans,w,len,l,r,n;
int cmp(const void*a,const void*b)
{
    int c=*(int*)a,d=*(int*)b;
    if (c<d) return -1;
    if (c>d) return 1;
    return 0;
}
int main()
{
    scanf("%d%d",&w,&n);
    for (int i=1;i<=n;++i) scanf("%d",&a[i]);
    qsort(a,n+1,sizeof(int),cmp);
    int t=w-a[1];
    len=n;
    while (a[len]>t) --len;
    ans=n-len;
    l=1;r=len;
    while (l<=r)
          if (l==r)
          {
                   ++ans;
                   break;
          }
          else
          if (a[l]+a[r]<=w)
          {
                          ++ans;
                          ++l; --r;
          }
          else
          {
              ++ans;
              --r;
          }
    printf("%d\n",ans);
    return 0;
}

C++ :

#include <iostream>
#include <algorithm>
using namespace std;
int a[30010];
int main()
{
    int n, w, count=0;
    cin>>w>>n;
    for (int i=0; i<n; i++)
        cin>>a[i];
    sort(a, a+n);
    for (int i=n-1, j=0; i>=j; i--)
    {
        if (a[i]==w) count++;
        else
        {
            if (a[i]+a[j]<=w)
            {
                count++;
                j++;
            }
            else count++;
        }
    }
    cout<<count<<endl;
    return 0;
}