k’th number

#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
#define for(i,x,y) for(int i=x;i<=y;i++)
#define  D "%d"
int n;int k,s,t=1,t2=1;
int a[1999],b[1999],c[1999],d[1999];
void dfs(int x,int ans){
	
	
	if(x>=n/2+1) return ;
	c[++t]=ans+a[x];
	dfs(x+1,a[x]+ans);
	dfs(x+1,ans);
	
}
void dfs2(int x,int ans){
	if(x>=n+1) return ;
	
	d[++t2]=ans+a[x];
	dfs2(x+1,a[x]+ans);
	dfs2(x+1,ans);
}
int check(int x)
{
	int ans=0;int t3=t2;
	for(i,1,t)
	{
		while(c[i]+d[t3]>=x&&t3>0)
		t3--;
		if(t3==0) break;
		ans+=t3;
	}
	return ans;
}
int main()
{
	scanf(D D,&n,&k);
	for(i,1,n)
	{
		scanf(D,&a[i]);
		s+=a[i];
	}
	c[1]=0;
	d[1]=0;
	dfs(1,0);
	dfs2(n/2+1,0);
	sort(c+1,c+t+1);
	sort(d+1,d+t2+1);
	/*for(i,1,t)
	printf(D " ",c[i]);
	printf("n");
	for(i,1,t2)
	printf(D " ",d[i]);*/
	int l=0,r=s+5;
	while(l<=r)
	{
		int mid=(l+r)>>1;
		int w=check(mid);
		if(w>(1<<n)-k) r=mid-1;
		else l=mid+1;
	}
	printf(D,r);
}