#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <queue>
#include <set>
using namespace std;

struct Dinic {
	static const int INF = 1e9;

	struct E {
		//to,容量,逆辺のindex
		int to, cap, rev;
		E(int t, int c, int r) {
			to = t;
			cap = c;
			rev = r;
		}
	};

	//最大頂点数
	int MAX_V;
	vector<vector<E>>G;
	Dinic(int max_v) {
		MAX_V = max_v;
		G.resize(MAX_V);
	}

	//有向辺
	inline void add_edge(int from, int to, int cap) {
		if (from == to)return;
		G[from].push_back(E(to, cap, G[to].size()));
		G[to].push_back(E(from, 0, G[from].size()-1));
	}

	//無向辺
	inline void add_undirected_edge(int from, int to, int cap) {
		if (from == to)return;
		G[from].push_back(E(to, cap, G[to].size()));
		G[to].push_back(E(from, cap, G[from].size()-1));
	}

	//深さ
	vector<int>level;

	//深さのラベル付け
	void bfs(int s) {
		level.assign(MAX_V, -1);
		queue<int> que;
		level[s] = 0;
		que.push(s);
		while (!que.empty()) {
			int v = que.front(); que.pop();
			for (int i = 0; i < G[v].size(); i++) {
				E &e = G[v][i];
				if (e.cap > 0 && level[e.to] < 0) {
					level[e.to] = level[v] + 1;
					que.push(e.to);
				}
			}
		}
	}

	//s -- v -- u -- t
	//tから深さ優先探索
	int dfs(int s, int u, int crr) {
		if (s == u || crr == 0)return crr;

		int sum = 0;

		for (int i = 0; i < G[u].size(); i++) {
			E& e = G[u][i];				//t側
			E& ee = G[e.to][e.rev];		//s側

			int v = e.to;
			if (level[v] >= level[u] || ee.cap <= 0)continue;

			int f = dfs(s, v, min(crr - sum, ee.cap));
			if (f <= 0)continue;

			//容量の更新
			ee.cap -= f;
			e.cap += f;

			//流量の更新
			sum += f;

			if (sum == crr)break;
		}

		return sum;
	}

	int max_flow(int s, int t) {
		int flow = 0;
		//tに流せなくなるまで
		while(1){
			bfs(s);
			if (level[t] < 0)return flow;
			flow += dfs(s, t, INF);
		}
	}
};


int main()
{
	int N; cin >> N;
	vector<int>A(N);
	for (int i = 0; i < N; i++) {
		cin >> A[i];
	}

	Dinic dnc(2502);
	for (int i = 0; i < N; i++) {
		dnc.add_edge(0,i+1,1);
		for (int j = 0; j < N; j++) {
			if (j == A[i])continue;
			dnc.add_edge(i + 1, N + j + 1, 1);
		}
		dnc.add_edge(N + i + 1, N*N + 1, 1);
	}

	int ans = dnc.max_flow(0,N*N+1);
	if (ans != N)cout << -1 << endl;
	else {
		for (int i = 1; i <= N; i++) {
			for (int j = 0; j < dnc.G[i].size(); j++) {
				if (dnc.G[i][j].to > i && dnc.G[i][j].cap == 0)cout << dnc.G[i][j].to - N - 1<< endl;
			}
		}
	}

    return 0;
}