#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, flag;
  cin >> n >> m;
  int l[m], ans[n], check[n];
  memset(ans, 0, sizeof(ans));
  memset(check, 0, sizeof(check));
  for (int i = 0; i < m; i++) cin >> l[i];
  for (int i = 0; i < m - 1; i++) {
    if (l[i + 1] > l[i]) {
      flag = 0;
      if (ans[l[i] - 1] != 0) {
        if (ans[l[i] - 1] != l[i + 1] - l[i]) {
          cout << "-1";
          return 0;
        } else
          flag = 1;
      }
      ans[l[i] - 1] = l[i + 1] - l[i];
      if (check[ans[l[i] - 1] - 1] == 0)
        check[ans[l[i] - 1] - 1] = 1;
      else if (flag == 0) {
        cout << "-1";
        return 0;
      }
    } else {
      flag = 0;
      if (ans[l[i] - 1] != 0) {
        if (ans[l[i] - 1] != l[i + 1] - l[i] + n) {
          cout << "-1";
          return 0;
        } else
          flag = 1;
      }
      ans[l[i] - 1] = l[i + 1] - l[i] + n;
      if (check[ans[l[i] - 1] - 1] == 0)
        check[ans[l[i] - 1] - 1] = 1;
      else if (flag == 0) {
        cout << "-1";
        return 0;
      }
    }
  }
  for (int i = 0; i < n; i++) {
    if (ans[i])
      cout << ans[i] << " ";
    else {
      for (int j = 0; j < n; j++)
        if (check[j] == 0) {
          cout << j + 1 << " ";
          check[j] = 1;
          break;
        }
    }
  }
  return 0;
}
