#!/usr/bin/env python3 import heapq def gnome_seq(A, H, n): R = [] i = 0 while i < len(A): if not len(H) == 0 and H[0] < A[i]: R.append(heapq.heappop(H)) else: R.append(A[i]) i += 1 while len(H) > 0: R.append(heapq.heappop(H)) return R if __name__ == "__main__": string = input().split() n = int(string[0]) m = int(string[1]) A = [] E = [False] * (n+1) for i in range(m): num = int(input()) A.append(num) E[num] = True H = [] for i in range(1, n + 1): if not E[i]: heapq.heappush(H, i) for n in gnome_seq(A, H, n): print(n)