#include <bits/stdc++.h>
using namespace std;
int v[200000];
set<int> g;
vector<int> av;
set<int> v2;
vector<int> o[2];
set<int> aux;
int main() {
  int n, m, p[2];
  cin >> n >> m;
  p[0] = p[1] = 0;
  for (int i = 0; i < n; i++) {
    cin >> v[i];
    v2.insert(v[i]);
    p[v[i] & 1]++;
  }
  if (n % 2) {
    cout << -1;
    return 0;
  }
  int x = (p[0] > p[1] ? 0 : 1);
  for (int i = 0; i < n; i++)
    if (v[i] % 2 != x) g.insert(v[i]);
  int i = (!x == 0 ? 2 : 1);
  int d = (p[x] - p[!x]) / 2;
  while (i <= m && d > 0) {
    if (g.find(i) == g.end()) {
      d--;
      av.push_back(i);
    }
    i += 2;
  }
  if (d != 0) {
    cout << -1;
    return 0;
  }
  for (int i = 0; i < n; i++)
    if (v[i] % 2 == x && av.size()) {
      v[i] = av.back();
      av.pop_back();
    }
  d = (p[x] - p[!x]) / 2;
  for (int i = 1; i <= n * 8 && i <= m; i++) {
    if (v2.find(i) == v2.end()) o[i & 1].push_back(i);
  }
  for (int i = 0; i < n; i++) {
    if (aux.find(v[i]) == aux.end()) {
      aux.insert(v[i]);
    } else {
      if (o[v[i] & 1].size()) {
        v[i] = o[v[i] & 1].back();
        o[v[i] & 1].pop_back();
        d++;
      } else {
        cout << -1;
        return 0;
      }
    }
  }
  cout << d << endl;
  for (int i = 0; i < n; i++) cout << v[i] << ' ';
  return 0;
}
