#include<bits/stdc++.h>
// #include<atcoder/modint>
// #include<atcoder/convolution>
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define F first
#define S second
#define rs resize
#define ft front()
#define bk back()
#define int long long
#define vi vector<int>
#define vvi vector<vector<int>>
#define pii pair<int, int>
#define vpii vector<pair<int, int>>
#define vc vector<char>
#define vb vector<bool>
#define mii map<int,int>
#define f0r(i,n) for(int i=0;i<n;i++)
#define FOR(i,k,n) for(int i=k;i<n;i++)
#define r0f(i,n) for(int i = n-1; i >= 0; i--)
#define R0F(i,k,n) for(int i = n-1; i >= k; i--)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define SUM(v) (accumulate(all(v), 0LL))
#define in(a) int a; cin>>a
#define in2(a,b) int a,b; cin>>a>>b
#define in3(a,b,c) int a,b,c; cin>>a>>b>>c
#define in4(a,b,c,d) int a,b,c,d; cin>>a>>b>>c>>d
#define vin(v,n); vi v(n); f0r(i,n){cin>>v[i];}
#define out(a) cout<<a<<'\n'
#define out2(a,b) cout<<a<<' '<<b<<'\n'
#define out3(a,b,c) cout<<a<<' '<<b<<' '<<c<<'\n'
#define out4(a,b,c,d) cout<<a<<' '<<b<<' '<<c<<' '<<d<<'\n'
#define pout(a) cout<<a.first<<' '<<a.second<<'\n'
#define vout(v) for(auto u : v){cout<<u<<' ';} cout<<endl
#define dout(a) cout<<a<<' '<<#a<<endl
#define dout2(a,b) cout<<a<<' '<<#a<<' '<<b<<' '<<#b<<endl
#define YN(x); if(x){cout<<"YES"<<'\n';}else{cout<<"NO"<<'\n';}
#define yn(x); if(x){cout<<"Yes"<<'\n';}else{cout<<"No"<<'\n';}
#define p2(x) (1LL << (x))
#define pct(x) (__builtin_popcountll((x)))
#define ist(x,y) (((x) >> (y)) & 1)
template<class T, class U> bool ckmin(T& a, const U& b) { return (T)b < a ? a = (T)b, 1 : 0; }
template<class T, class U> bool ckmax(T& a, const U& b) { return a < (T)b ? a = (T)b, 1 : 0; }
const int leg = 1e9 + 7;
const int mod = 998244353;
using namespace std;
// using namespace atcoder;
// using mint = modint998244353;
// using mint = modint1000000007;
const int mxp = 1e4 + 5;
// mint fact[mxn], inv[mxn];
// mint C(int n, int r){return fact[n] * inv[n-r] * inv[r];}
// mint snb(int n, int r){return C(n + r, n);}
vi g;
struct info{
int a,b,c;
bool operator <(const info &x) const{
return a < x.a;
}
};
void solve(vi a, vi b, int c){
bool f = 0; int n = a.size(); if(b[0]<a[0]){f0r(i,n)a[i]=-a[i],b[i]=-b[i]; reverse(all(a)); reverse(all(b)); f=1;}
vpii w; for(auto u : a)w.eb(u,1); for(auto u : b)w.eb(u,-1); sort(all(w)); //for(auto u : w)pout(u);
vi tmp, ps(2*n); ps[0]=w[0].S; FOR(i,1,2*n)ps[i]=ps[i-1]+w[i].S; //vout(ps);
for(int d = c; d - c + 1 <= n; d+=c){
f0r(i,2*n){
if(w[i].S==1 && ps[i] > d-c && ps[i] <= d)tmp.pb(w[i].F);
else if(w[i].S==-1 && ps[i] >= d-c && ps[i]<d)tmp.pb(w[i].F);
}
}
if(f){for(auto &u : tmp)u=-u;} for(auto u : tmp)g.pb(u);
}
signed main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
//ifstream cin(".in");
//ofstream cout(".out");
// fact[0]=1;FOR(i,1,mxn)fact[i]=fact[i-1]*i;inv[mxn-1]=fact[mxn-1].inv();r0f(i,mxn-1)inv[i]=inv[i+1]*(i+1);
in2(n,c); vin(a,n); vin(b,n); sort(all(a)); sort(all(b)); vi d(mxp); f0r(i,n){
if(a[i] < b[i])d[a[i]]++, d[b[i]]--; else d[b[i]]++,d[a[i]]--;
}
int ans = 0, cur = 0; f0r(i,mxp){
cur += d[i]; ans += (cur + c - 1) / c;
} out(ans);
vi x, y; int p1 = 0, p2 = 0; while(p1 < n || p2 < n){
if(p1 == n)y.pb(b[p2]),p2++;
else if(p2==n)x.pb(a[p1]),p1++;
else if(a[p1] < b[p2])x.pb(a[p1]),p1++;
else y.pb(b[p2]),p2++;
if(x.size()==y.size()){
solve(x,y,c); x.clear();y.clear();
}
}
vout(g);
}
