func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int n;     cin >> n;     vector<int> a(n + 1, 0), ans(n + 1, -1), visited(n + 1, 0);     for (int i = 1; i <= n; i++) {       cin >> a[i];       if (a[i] > a[i - 1]) {         ans[i] = a[i - 1];         visited[a[i]] = 1;       }     }     int j = 1;     for (int i = 1; i <= n; i++) {       if (ans[i] == -1) {         while (j <= n && visited[j]) j++;         ans[i] = j;         visited[j] = 1;       }     }     for (int i = 1; i <= n; i++) cout << ans[i] <<    ;     return 0;   }   