#include <bits/stdc++.h>
using namespace std;
int n, m, even, odd, a[200100], need, ans;
set<int> st, st2, stEven, stOdd;
queue<int> q, q2;
bool changed[200100];
int main() {
  scanf("%d %d", &n, &m);
  for (int i = 0; i < n; i++) {
    scanf("%d", &a[i]);
    if (a[i] % 2 == 0)
      even++;
    else
      odd++;
  }
  if (odd == even) {
    for (int i = 0; i < n; i++) {
      if (a[i] % 2 == 0)
        st.insert(a[i]);
      else
        st2.insert(a[i]);
    }
    need = n / 2;
    for (int i = 2; i <= m; i += 2) {
      if (st.find(i) == st.end()) {
        q.push(i);
        need--;
        if (need == 0) break;
      }
    }
    need = n / 2;
    for (int i = 1; i <= m; i += 2) {
      if (st2.find(i) == st2.end()) {
        q2.push(i);
        need--;
        if (need == 0) break;
      }
    }
    for (int i = 0; i < n; i++) {
      if (a[i] % 2 == 0) {
        if (stEven.find(a[i]) == stEven.end()) {
          stEven.insert(a[i]);
        } else {
          if (q.empty()) {
            printf("-1\n");
            return 0;
          }
          ans++;
          a[i] = q.front();
          q.pop();
        }
      } else {
        if (stOdd.find(a[i]) == stOdd.end()) {
          stOdd.insert(a[i]);
        } else {
          if (q2.empty()) {
            printf("-1\n");
            return 0;
          }
          ans++;
          a[i] = q2.front();
          q2.pop();
        }
      }
    }
  } else {
    for (int i = 0; i < n; i++) {
      if (a[i] % 2 == 0)
        st.insert(a[i]);
      else
        st2.insert(a[i]);
    }
    need = n / 2;
    for (int i = 2; i <= m; i += 2) {
      if (st.find(i) == st.end()) {
        q.push(i);
        need--;
        if (need == 0) break;
      }
    }
    need = n / 2;
    for (int i = 1; i <= m; i += 2) {
      if (st2.find(i) == st2.end()) {
        q2.push(i);
        need--;
        if (need == 0) break;
      }
    }
    for (int i = 0; i < n; i++) {
      if (odd > even) {
        if (a[i] % 2 == 1) {
          if (stOdd.find(a[i]) == stOdd.end()) {
            stOdd.insert(a[i]);
          } else {
            if (q.empty()) {
              printf("-1\n");
              return 0;
            }
            odd--;
            even++;
            ans++;
            changed[i] = 1;
            a[i] = q.front();
            q.pop();
          }
        }
      } else if (even > odd) {
        if (a[i] % 2 == 0) {
          if (stEven.find(a[i]) == stEven.end()) {
            stEven.insert(a[i]);
          } else {
            if (q2.empty()) {
              printf("-1\n");
              return 0;
            }
            even--;
            odd++;
            ans++;
            changed[i] = 1;
            a[i] = q2.front();
            q2.pop();
          }
        }
      } else {
        if (a[i] % 2 == 0) {
          if (stEven.find(a[i]) == stEven.end()) {
            stEven.insert(a[i]);
          } else {
            if (q.empty()) {
              printf("-1\n");
              return 0;
            }
            ans++;
            changed[i] = 1;
            a[i] = q.front();
            q.pop();
          }
        } else {
          if (stOdd.find(a[i]) == stOdd.end()) {
            stOdd.insert(a[i]);
          } else {
            if (q2.empty()) {
              printf("-1\n");
              return 0;
            }
            ans++;
            changed[i] = 1;
            a[i] = q2.front();
            q2.pop();
          }
        }
      }
    }
  }
  for (int i = 0; i < n; i++) {
    if (a[i] % 2 == 1 && odd > even && !changed[i]) {
      if (q.empty()) {
        printf("-1\n");
        return 0;
      }
      odd--;
      even++;
      ans++;
      a[i] = q.front();
      q.pop();
    } else if (a[i] % 2 == 0 && even > odd && !changed[i]) {
      if (q2.empty()) {
        printf("-1\n");
        return 0;
      }
      even--;
      odd++;
      ans++;
      a[i] = q2.front();
      q2.pop();
    }
  }
  st.clear();
  st2.clear();
  for (int i = 0; i < n; i++) {
    if (st.find(a[i]) == st.end()) {
      st.insert(a[i]);
    } else {
      if (a[i] % 2 == 0) {
        if (q.empty()) {
          printf("-1\n");
          return 0;
        }
        ans++;
        a[i] = q.front();
        q.pop();
      } else {
        if (q2.empty()) {
          printf("-1\n");
          return 0;
        }
        ans++;
        a[i] = q2.front();
        q2.pop();
      }
    }
  }
  if (even != odd) {
    printf("-1\n");
    return 0;
  }
  printf("%d\n", ans);
  for (int i = 0; i < n; i++) printf("%d ", a[i]);
  printf("\n");
  return 0;
}
