#include<iostream>
#include<string>
#include<algorithm>
#include<string>
#include<cstring>
#include<cmath>
using namespace std;
int n;
int a[10000],b[10000];
int sum=0;
void init()
{
	cin>>n;
	for(int i=1;i<=n;i++)
		cin>>a[i];
}
void dfs(int m,int k)
{
	if(m==n+1)return ;
	int p=k^a[m];
	if(p==0)
	{
		sum++;
		b[m]=m;
		cout<<sum<<endl;
		for(int i=1;i<=n;i++)
		if(b[i])cout<<b[i]<<' ';
		cout<<endl;
		exit(0);
	}
	else 
	{
		sum++;
		b[m]=m;
		dfs(m+1,p);
		sum--;
		b[m]=0;
	}
	dfs(m+1,k);
}
int main()
{
	freopen("asm_contribute.in","r",stdin);
	freopen("asm_contribute.out","w",stdout);
	memset(a,0,sizeof(a));
	memset(b,0,sizeof(b));
	init();
	dfs(1,0);
	return 0;
}