#include <bits/stdc++.h>
using namespace std;
template <class T1>
void deb(T1 e1) {
  cout << e1 << endl;
}
template <class T1, class T2>
void deb(T1 e1, T2 e2) {
  cout << e1 << " " << e2 << endl;
}
template <class T1, class T2, class T3>
void deb(T1 e1, T2 e2, T3 e3) {
  cout << e1 << " " << e2 << " " << e3 << endl;
}
template <class T1, class T2, class T3, class T4>
void deb(T1 e1, T2 e2, T3 e3, T4 e4) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << endl;
}
template <class T1, class T2, class T3, class T4, class T5>
void deb(T1 e1, T2 e2, T3 e3, T4 e4, T5 e5) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << " " << e5 << endl;
}
template <class T1, class T2, class T3, class T4, class T5, class T6>
void deb(T1 e1, T2 e2, T3 e3, T4 e4, T5 e5, T6 e6) {
  cout << e1 << " " << e2 << " " << e3 << " " << e4 << " " << e5 << " " << e6
       << endl;
}
int n, m, e, o, ans, arr[300000];
bool mark[500000 + 7];
vector<int> even;
vector<int> odd;
map<int, bool> rep;
bool solve() {
  int v, a, i, j, k;
  for (i = 0; i < n; i++) {
    v = arr[i];
    if (rep[v]) {
      if (e == o) {
        if (v % 2 == 0) {
          if (even.size() == 0) return 0;
          arr[i] = even.back();
          even.pop_back();
          ans++;
        } else {
          if (odd.size() == 0) return 0;
          arr[i] = odd.back();
          odd.pop_back();
          ans++;
        }
      } else if (e > o) {
        if (odd.size() == 0) return 0;
        arr[i] = odd.back();
        odd.pop_back();
        ans++;
        a = (v % 2 == 0);
        e -= a;
        o += a;
      } else {
        if (even.size() == 0) return 0;
        arr[i] = even.back();
        even.pop_back();
        ans++;
        o -= (v % 2 == 1);
        e += (v % 2 == 1);
      }
    } else {
      rep[v] = 1;
    }
  }
  for (i = 0; i < n; i++) {
    v = arr[i];
    if (e == o) break;
    if (e > o) {
      if (odd.size() == 0) return 0;
      if (v % 2 == 0) {
        arr[i] = odd.back();
        odd.pop_back();
        ans++;
        e--;
        o++;
      }
    } else {
      if (even.size() == 0) return 0;
      if (v % 2 == 1) {
        arr[i] = even.back();
        even.pop_back();
        ans++;
        e++;
        o--;
      }
    }
  }
  return 1;
}
int main() {
  int i, j, k;
  e = o = 0;
  scanf("%d %d", &n, &m);
  for (i = 0; i < n; i++) {
    scanf("%d", &arr[i]);
    if (arr[i] % 2 == 0)
      e++;
    else
      o++;
    if (arr[i] <= 500000) mark[arr[i]] = 1;
  }
  for (i = 1; i <= m and i <= 500000; i++) {
    if (mark[i] == 0) {
      if (i % 2 == 0)
        even.push_back(i);
      else
        odd.push_back(i);
    }
  }
  ans = 0;
  if (!solve()) {
    printf("-1\n");
  } else {
    printf("%d\n", ans);
    for (i = 0; i < n; i++) {
      printf("%d ", arr[i]);
    }
  }
  return 0;
}
