import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.util.Stack;
import java.util.ArrayList;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author cunbidun
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        ALimitedInsertion solver = new ALimitedInsertion();
        solver.solve(1, in, out);
        out.close();
    }

    static class ALimitedInsertion {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            int[] a = in.nextIntArray(n, 1);
            Stack<Integer> stack = new Stack<>();
            ArrayList<Integer> num = new ArrayList<>();
            num.add(0);
            for (int i = 1; i <= n; i++) {
                num.add(a[i]);
            }
            while (num.size() > 1) {
                boolean d = false;
                for (int j = num.size() - 1; j >= 1; j--) {
                    if (num.get(j) == j) {
                        stack.push(j);
                        num.remove(j);
                        d = true;
                        break;
                    }
                }
                if (!d) {
                    out.println(-1);
                    return;
                }

            }

//        if (stack.size() != n) {
//            out.println(-1);
//            return;
//        }
            while (!stack.empty()) {
                out.println(stack.pop());
            }
        }

    }

    static class InputReader extends InputStream {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (numChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public int[] nextIntArray(int length, int stIndex) {
            int[] arr = new int[length + stIndex];
            for (int i = stIndex; i < stIndex + length; i++)
                arr[i] = nextInt();
            return arr;
        }

        private static boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

    }
}



Measured memory_bytes: 23252