#include <stdio.h>

int a[103000], chk[103000], res[103000];

int main(void) {
    int n, m, rcnt = 0, p = 0;
    scanf("%d %d", &n, &m);
    for (int i = 0; i < m; i++) {
        scanf("%d", &a[i]);
        chk[a[i]] = 1;
    }
    for (int i = 1; i <= n; i++) {
        if (chk[i]) continue;
        while (p < m && i > a[p]) {
            res[rcnt++] = a[p];
            p++;
        }
        res[rcnt++] = i;
    }
    if (rcnt != n) return 1;
    for (int i = 0; i < n; i++) {
        printf("%d\n", res[i]);
    }
    return 0;
}