AGC 032 | A - Limited Insertion

#include <bits/stdc++.h>

#include <atcoder/all>

using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using uint = unsigned int;
using ull = unsigned long long;
const int MOD = 1e9 + 7;

int main() {
  ll n;
  cin >> n;
  vector<ll> b(n);
  for (int i = 0; i < n; i++) {
    cin >> b[i];
  }
  vector<int> ans;
  for (int i = n; i >= 1; i--) {
    bool found = false;
    for (int j = i; j >= 1; j--) {
      if (b[j - 1] == j) {
        ans.insert(ans.begin(), j);
        b.erase(b.begin() + (j - 1));
        found = true;
        break;
      }
    }
    if (!found) {
      cout << -1 << endl;
      return 0;
    }
  }
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i] << endl;
  }
}