#include<iostream>
#include<cstring>
#include<cstdio>
#include<cstdlib>
#include<queue>
#include<vector>
#include<stack>
#include<cmath>
#include<algorithm>
#include<map>
#include<set>
using namespace std;
struct weixing
{
	long long data;
	int num;
};
weixing a[1001];
int N;
void read()
{
	cin>>N;
	for(int i=1;i<=N;i++)
	{
		cin>>a[i].data;
		a[i].num=i;
	}	
}
bool cmp(weixing a,weixing b)
{
	return a.data<b.data;
}
bool judge()
{
	sort(a+1,a+1+N,cmp);
	for(int i=2;i<=N;i++)
	{
		if(a[i-1].data==a[i].data)
		{
			cout<<2<<endl;
			cout<<a[i-1].num<<a[i].num<<endl;
			return true;
		}
	}
	return false;
}
void sovle()
{
	if(judge()) return;
	else
	{
		for(int i=1;i<=N;i++)
		{
			for(int j=i+1;j<=N;j++)
			{
				for(int k=j+1;k<=N;k++)
				{
					if(a[i].data^a[j].data^a[k].data==0)
					{
						cout<<3<<endl;
						cout<<a[i].num<<a[j].num<<a[k].num<<endl;
						return;
					}
					for(int p=k+1;k<=N;k++)
					{
						if(a[i].data^a[j].data^a[k].data^a[p].data==0)
						{
							cout<<3<<endl;
							cout<<a[i].num<<a[j].num<<a[k].num<<a[p].num<<endl;
							return;
						}
						for(int m=1;m<=N;m++)
						{
							if(a[i].data^a[j].data^a[k].data^a[p].data^a[m].data==0)
							{
								cout<<4<<endl;
								cout<<a[i].num<<a[j].num<<a[k].num<<a[p].num<<a[m].data<<endl;
								return;
							}
							
						}
					}
				}
			}
		}
	}
}
bool du()
{
	for(int i=2;i<=N;i++)
	{
		if(a[i].data!=a[i-1].data) return false;
	}
	return true;
}
int main()
{
	freopen("asm_contribute.in","r",stdin);
	freopen("asm_contribute.out","w",stdout);
	read();
	if(du())
	{
		cout<<2<<endl;
		cout<<1<<' '<<2<<endl;
		return 0;
	}
	sovle(); 
	return 0;
}