"use strict";
function Main(input) {
    let cin = new Inputer(input);
    let N = cin.getInt(), B = cin.getIntArray(N);
    let ans = [];
    while (B.length > 0) {
        let f = false;
        for (let n = N - 1; n >= 0; n--) {
            if (B[n] == n + 1) {
                ans.push(B[n]);
                B.splice(n, 1);
                f = true;
                break;
            }
        }
        if (!f) {
            console.log(-1);
            return;
        }
    }
    console.log(ans.reverse().join('\n'));
}
class Inputer{constructor(t){if(typeof t=='undefined')throw new Error('引数（stdin）を省略できません！');this.cnt=0,this.items=t.split(/\n|\s/)}getInt(){return this.items[this.cnt++]-0}getIntArray(t){if(typeof t=='undefined')throw new Error('引数（1以上）を省略できません！');let r=new Array(t);for(let e=0;e<t;e++)r[e]=this.getInt();return r}getStr(){return this.items[this.cnt++]}getStrArray(t){if(typeof t=='undefined')throw new Error('引数（1以上）を省略できません！');let r=new Array(t);for(let e=0;e<t;e++)r[e]=this.getStr();return r}}
if (typeof window == "undefined") Main(require("fs").readFileSync("/dev/stdin", "utf8"));