#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const long long INFF = 0x3f3f3f3f3f3f3f3fll;
const long long M = 1e9 + 7;
const long long maxn = 1e6 + 7;
const double pi = acos(-1.0);
const double eps = 0.00000001;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
template <typename T>
inline T abs(T a) {
  return a > 0 ? a : -a;
}
template <typename T>
inline T powMM(T a, T b) {
  T ret = 1;
  for (; b; b >>= 1ll, a = (long long)a * a % M)
    if (b & 1) ret = (long long)ret * a % M;
  return ret;
}
int A[maxn];
map<int, int> S;
vector<int> del, ini[2], have[2];
int cnt[2], ans;
int main() {
  int n, m, i, j;
  scanf("%d%d", &n, &m);
  m = min(m, n * 2);
  for (i = 1; i <= n; i++) scanf("%d", &A[i]);
  for (i = 1; i <= n; i++) {
    if (S.count(A[i])) {
      del.push_back(i);
      ans++;
    } else {
      S[A[i]] = i, cnt[A[i] & 1]++;
      ini[A[i] & 1].push_back(i);
    }
  }
  for (i = 0; i < 2; i++) {
    sort(ini[i].begin(), ini[i].end());
    for (j = 0; j < (int)ini[i].size() - n / 2; j++) {
      S.erase(A[ini[i][j]]);
      cnt[i]--;
      ans++;
      del.push_back(ini[i][j]);
    }
  }
  j = 0;
  for (i = 1; i <= m; i++) {
    if (!S.count(i)) {
      if (cnt[i & 1] != n / 2) {
        cnt[i & 1]++;
        A[del[j++]] = i;
      }
    }
  }
  if (cnt[0] != n / 2 || cnt[1] != n / 2) return 0 * puts("-1");
  printf("%d\n", ans);
  for (i = 1; i <= n; i++) printf("%d ", A[i]);
  return 0;
}
