#include <bits/stdc++.h>
using namespace std;
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n; long long k;
    if(!(cin>>n>>k)) return 0;
    vector<long long> a(n), b(n);
    for(int i=0;i<n;i++) cin>>a[i];
    for(int i=0;i<n;i++) cin>>b[i];
    long long base = 0; 
    vector<int> ra, rb;
    ra.reserve(n); rb.reserve(n);
    for(int i=0;i<n;i++){
        base += a[i] / k;
        ra.push_back(int(a[i] % k));
    }
    for(int i=0;i<n;i++){
        base += b[i] / k;
        rb.push_back(int(b[i] % k));
    }
    sort(ra.begin(), ra.end(), greater<int>());
    multiset<int> ms;
    for(int x: rb) ms.insert(x);
    long long extra = 0; 
    for(int r : ra){
        if(ms.empty()) {
            if(r==0) extra += 0; else extra += 1;
            continue;
        }
        int need = int(k - r);
        auto it = ms.upper_bound(need); 
        if(it==ms.begin()){
            auto it2 = ms.begin();
            int val = *it2;
            ms.erase(it2);
            if(r + val == 0) extra += 0;
            else if(r + val <= (int)k) extra += 1;
            else extra += 2; // r+val > k
        } else {
            --it;
            int val = *it;
            ms.erase(it);
            if(r + val == 0) extra += 0;
            else extra += 1; 
        }
    }
    cout << (base + extra) << '\n';
    return 0;
}