import java.util.Arrays;
import java.util.Scanner;

class Main {
	public static void main(String[] args) {
		new Main().run();
	}
	
	int target(int[] A,int[] ans) {
		int p=0;
		while(p<ans.length&&(ans[p]!=-1||A[p]==-1))++p;
		if(p<ans.length)return A[p];
		else {
			for(int i=0;i<A.length;++i) {
				boolean flag=true;
				for(int j=0;j<ans.length;++j)flag&=ans[j]!=i;
				if(flag)return i;
			}
			throw new AssertionError();
		}
	}
	
	void run() {
		Scanner sc=new Scanner(System.in);
		int N=sc.nextInt();
		int[] A=new int[N];
		for(int i=0;i<N;++i) {
			A[i]=sc.nextInt();
			if(!(0<=A[i]&&A[i]<N))A[i]=-1;
		}
		boolean ng=true;
		for(int i=0;i<N;++i)ng&=A[i]==A[0];
		ng&=0<=A[0]&&A[0]<N;
		if(ng) {
			System.out.println(-1);
			return;
		}
		int[] ans=new int[N];
		Arrays.fill(ans, -1);
		for(int i=0;i<N;++i) {
			int target=target(A, ans);//targetを誰かに塗る
			int p=0;
			while(A[p]==target||ans[p]!=-1)++p;
			ans[p]=target;
			for(int j=0;j<N;++j)if(ans[j]==-1&&A[j]==target)A[j]=-1;
		}
		for(int i=0;i<N;++i)System.out.println(ans[i]);
	}
	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}