2020-10-25

7-9

#include<bits/stdc++.h>

#define vint vector<int>
#define vstr vector<string>
#define vll vector<long long>
#define ll long long
#define ull unsigned long long
#define pf printf
#define sf scanf
#define sfd(n) scanf("%d", &n)
#define sfc(n) scanf("%c", &n)
#define sflf(n) scanf("%lf", &n)
#define sfll(n) scanf("%lld", &n)
#define pfd(n) printf("%d", n)
#define pfc(n) printf("%c", n)
#define pflf(n) printf("%lf", n)
#define pfll(n) printf("%lld", n)
#define pft	printf("\t")
#define pfn printf("\n")
#define pfk printf(" ")
#define PI 3.1415926
#define MAX 100010
#define MOD ((long long)1e9+7)

using namespace std;

int a[MAX];

struct D{
	int num;
	int p;
};
D data[MAX];

void F(int x, int y) {
	int root = x;
	int cnt = 1;
	while( root!=-1 ) {
		if( data[root].p ) {
			cnt = data[root].p+1;
			break;
		}
		root = a[root];
		cnt++;
	}
	data[y].num = y;
	data[y].p = cnt;
}

int main() {
	int n;
	cin >> n;
	for( int i=1; i<=n; i++ ) {
		cin >> a[i];
	}
	for( int i=1; i<=n; i++ ) {
		F(a[i], i);
	}
	sort(data+1, data+n+1, [](D a, D b) {
		if( a.p>b.p ) {
			return true;
		}else if( a.p==b.p ){
			return a.num<b.num;
		}
		return false;
	});
	int min = data[1].p;
	pfd(min);
	pfn;
	for( int i=1; i<=n; i++ ) {
		
//		cout << data[i].num << " " << data[i].p << endl;
		
		if( data[i].p!=min ) {
			break;
		}
		if( i>1 ) pfk;
		pfd(data[i].num );
	}

	return 0;
}