#include <bits/stdc++.h>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define ios ios_base::sync_with_stdio(false);cin.tie(NULL)
#define ld long double
#define li __int128

using namespace std;

mt19937 rng(time(NULL));
int main()
{
	int n;
	scanf("%i",&n);
	vector<bool> in(n);
	int sm=0;
	vector<int> c(n);
	for(int i=0;i<n;i++){
		scanf("%i",&c[i]);
	}
	while(1){
		fill(all(in),0);
		sm=0;
		for(int i=0;i<n/2;i++){
			int x=rng()%n;
			while(in[x])x=rng()%n;
			in[x]=1;
			sm+=c[x];
		}
		int treba=1e9;
		vector<pair<int,int>> aa,bb;
		while(1){
			aa.clear(),bb.clear();
			for(int i=0;i<n;i++){
				if(in[i])aa.pb({c[i],i});
				else bb.pb({c[i],i});
			}
			sort(all(aa));
			sort(all(bb));
			int j=sz(bb)-1;
			pair<int,int> sta={-1,-1};
			int bst=abs(sm-treba);
			for(int i=0;i<sz(aa);i++){
				int ns=sm-aa[i].f+bb[j].f;
				int xx=abs(ns-treba);
				if(xx<bst){
					bst=xx;
					sta={aa[i].s,bb[j].s};
				}
				while(j>0){
					int nns=sm-aa[i].f+bb[j-1].f;
					int xxx=abs(nns-treba);
					if(xxx>xx)break;
					ns=nns;
					xx=xxx;
					j--;
					if(xx<bst){
						bst=xx;
						sta={aa[i].s,bb[j].s};
					}
				}
			}
			//printf("Swap %i %i!  %i\n",sta.f,sta.s,sm);
			if(sta.f==-1)break;
			in[sta.f]=0;
			in[sta.s]=1;
			sm-=c[sta.f];
			sm+=c[sta.s];
			//printf("sled: %i\n",sm);
			if(bst==0){
				printf("%i",n/2);
				for(int i=0;i<n;i++){
					if(in[i]){
						printf(" %i",i+1);
					}
				}
				printf("\n");
				return 0;
			}
		}
	}
	return 0;
}