#include <bits/stdc++.h>
using namespace std;
long long MOD = 1e9 + 7;
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  map<int, int> count;
  int n, m;
  cin >> n >> m;
  int a[n + 1];
  stack<pair<int, int> > values;
  int x[2];
  x[0] = 0;
  x[1] = 0;
  stack<int> y[2];
  for (int i = 0; i < n; i++) {
    cin >> a[i + 1];
    count[a[i + 1]]++;
    if (count[a[i + 1]] > 1) {
      values.push(make_pair(a[i + 1], i + 1));
    }
    x[a[i + 1] % 2]++;
  }
  for (int i = 1; i < min(m, 400000) + 1; i += 2) {
    if (count[i] == 0) {
      y[1].push(i);
    }
  }
  for (int i = 2; i < min(m, 400000) + 1; i += 2) {
    if (count[i] == 0) {
      y[0].push(i);
    }
  }
  int c, d;
  long long ans = 0;
  while (!values.empty()) {
    c = values.top().first;
    d = values.top().second;
    values.pop();
    x[c % 2]--;
    if (x[0] > x[1]) {
      if (y[1].empty()) {
        cout << -1 << '\n';
        return 0;
      }
      a[d] = y[1].top();
      y[1].pop();
      ans++;
      x[1]++;
    } else {
      if (y[0].empty()) {
        cout << -1 << '\n';
        return 0;
      }
      a[d] = y[0].top();
      y[0].pop();
      ans++;
      x[0]++;
    }
  }
  for (int i = 1; i < n + 1 && !(x[0] == x[1]); i++) {
    if (x[0] > x[1]) {
      if (y[1].empty()) {
        cout << -1 << '\n';
        return 0;
      }
      if (a[i] % 2 == 0) {
        a[i] = y[1].top();
        y[1].pop();
        ans++;
        x[1]++;
        x[0]--;
      }
    } else {
      if (y[0].empty()) {
        cout << -1 << '\n';
        return 0;
      }
      if (a[i] % 2 == 1) {
        a[i] = y[0].top();
        y[0].pop();
        ans++;
        x[0]++;
        x[1]--;
      }
    }
  }
  if (x[0] != x[1]) {
    cout << -1 << '\n';
    return 0;
  }
  cout << ans << '\n';
  for (int i = 1; i < n + 1; i++) {
    cout << a[i] << " ";
  }
}
