package main

import (
	"fmt"
)
import (
	"bufio"
	"os"
	"strconv"
)

func main() {

	N := nextInt()
	var used = make([]bool, N)
	var ans = make([]int, N)

	for i := 0; i < N; i++ {
		l := nextInt()
		hit := false
		for k := 0; k < N; k++ {
			if k == l {
				continue
			}
			if !used[k] {
				ans[i] = k
				hit = true
				used[k] = true
				break
			}
		}
		if !hit {
			fmt.Println(-1)
			return
		}
	}
	for i := 0; i < N; i++ {
		fmt.Println(ans[i])
	}
}

var s = bufio.NewScanner(os.Stdin)

func next() string {
	s.Split(bufio.ScanWords)
	s.Scan()
	return s.Text()
}
func nextLine() string {
	s.Split(bufio.ScanLines)
	s.Scan()
	return s.Text()
}

func nextInt() int {
	i, e := strconv.Atoi(next())
	if e != nil {
		panic(e)
	}
	return i
}
func nextLong() int64 {
	i, e := strconv.ParseInt(next(), 10, 64)
	if e != nil {
		panic(e)
	}
	return i
}