#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <array>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
#include <memory>
#include <regex>
using namespace std;

set<int>::iterator nextPosition(const set<int>& x, int curr)
{
    auto it = x.lower_bound(curr);
    if(it == x.end())
        return x.begin();
    else
        return it;
}

set<int>::iterator prevPosition(set<int>& x, int curr)
{
    auto it = x.upper_bound(curr);
    if(it == x.begin())
        return --x.end();
    else
        return --it;
}

int getDiff(int a, int b, int len)
{
    if(a <= b)
        return b - a;
    else
        return len - a + b;
}

int main()
{
    int n, len;
    cin >> n >> len;
    set<int> x, y;
    for(int i=0; i<n; ++i){
        int a;
        cin >> a;
        x.insert(a);
    }
    for(int i=0; i<n; ++i){
        int a;
        cin >> a;
        y.insert(a);
    }

    int curr = *x.begin();
    long long ans = curr;
    x.erase(x.begin());
    for(int i=0; i<n-1; ++i){
        auto it1 = nextPosition(y, curr);
        auto it2 = nextPosition(x, *it1);
        it1 = prevPosition(y, *it2);

        ans += getDiff(curr, *it1, len);
        curr = *it1;
        y.erase(it1);
        ans += getDiff(curr, *it2, len);
        curr = *it2;
        x.erase(it2);
    }
    ans += getDiff(curr, *y.begin(), len);
    cout << ans << endl;

    return 0;
}