#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int N, A[50];
bool used[50], eUsed[50][50], reUsed[50][50];

struct E{
    int to, cap, rev;
};

vector<E> G[50];

void add(int from, int to){
    G[from].push_back(E{to,1,(int)G[to].size()});
    G[to].push_back(E{from,0,(int)G[from].size() - 1});
}

int dfs(int v, int f){
    if(v == 2*N+1) return f;
    used[v] = 1;
    for(auto &e : G[v]){
        if(!used[e.to] && e.cap > 0){
            int d = dfs(e.to, min(e.cap, f));
            if(d > 0){
                e.cap -= d;
                G[e.to][e.rev].cap += d;
                return d;
            }
        }
    }
    return 0;
}

int get(){
    int f = 1, res = 0;
    while(f){
        MEM(used, 0);
        f = dfs(2 * N, INT_MAX);
        res += f;
    }
    return res;
}


int main(){
    cin >> N;
    rep(i, N){
        cin >> A[i];
        rep(j, N)if(j != A[i])
            add(i, N+j);
            
        add(2 * N, i);
        add(N + i, 2 * N + 1);
    }

    int cnt = get();
    if(cnt == N){
        rep(i, N){
            each(e, G[i]){
                int j = e.to - N;
                if(0 <= j && j < N && !e.cap){
                    eUsed[i][j] = 1;
                }
            }
            each(e, G[N+i]){
                int j = e.to;
                if(0 <= j && j < N && !e.cap)
                    reUsed[j][i] = 1;
            }
        }
        rep(i, N)rep(j, N){
            if(!reUsed[i][j] && eUsed[i][j]){
                cout << j << endl;
            }
        }
    } else{
        puts("-1");
    }
}