#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
const int inf = 0x3f3f3f3f;
int b[maxn];
int a[maxn];
int ma[maxn];
int pre[maxn * 10];
int _find(int x) { return x == pre[x] ? x : pre[x] = _find(pre[x]); }
void _union(int x, int y) {
  x = _find(x), y = _find(y);
  if (x < y)
    pre[x] = y;
  else
    pre[y] = x;
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < maxn * 10; ++i) pre[i] = i;
  for (int i = 1; i <= n; ++i) {
    scanf("%d", &a[i]);
    ma[i] = max(ma[i - 1], a[i]);
  }
  bool flag = true;
  int x = 0;
  for (int i = n; i > 0; --i) {
    if (a[i] > ma[i - 1])
      b[i] = ma[i - 1];
    else
      b[i] = a[i] + 1;
    b[i] = _find(b[i]);
    _union(b[i], b[i] + 1);
    _union(a[i], a[i] + 1);
    x = max(x, a[i]);
  }
  if (!flag)
    puts("-1");
  else {
    for (int i = 1; i <= n; ++i) printf("%d%c", b[i], i == n ? '\n' : ' ');
  }
  return 0;
}
