#include<iostream>
#include<cstring>
#include<cstdio>
#include<string>
#include<algorithm>
#include<cmath>
#include<utility>
#include<stdio.h>
#include<cstdlib>
#include<iomanip>	//cout<<setiosflags(ios::fixed)<<setprecision(2);
#include<ctime> //double a=(double)clock();	cout<<a<<endl;
#include<vector>
#include<queue>
using namespace std;
inline int read()
{
	int x=0,ff=1;char ch=getchar();
	while(ch>'9'||ch<'0'){if(ch=='-')ff=-1;ch=getchar();}
	while(ch<='9'&&ch>='0'){x=x*10+ch-'0';ch=getchar();}
	return ff*x;
}
int N;
long long sum[1010];
struct number
{
	long long v;
	int id;
	bool friend operator<(const number &A,const number &B)
	{return A.v<B.v;}
}num[1010];
inline bool mycmp(const number &A,const number &B)
{return A.v<B.v;}
int main()
{
	freopen("asm_contribute.in","r",stdin);
	freopen("asm_contribute.out","w",stdout);
	N=read();
	for(int i=1;i<=N;i++)
		num[i].v=read(),num[i].id=i;
	for(int i=1;i<=N;i++)
		for(int j=i+1;j<=N;j++)
			if(num[i].v==num[j].v)
			{
				printf("%d\n",2);
				printf("%d %d\n",num[i].id,num[j].id);
				return 0;
			}
	sort(num+1,num+1+N,mycmp);
	do
	{
		for(int i=1;i<=N;i++)
		{
			sum[i]=sum[i-1]^num[i].v;
			if(sum[i]==0)
			{
				printf("%d\n",i);
				for(int j=1;j<=i;j++)
					printf("%d ",num[j].id);
				printf("\n");
				return 0;
			}
		}
	}while(next_permutation(num+1,num+1+N));
	return 0;
}