#include<bits/stdc++.h>
using namespace std;

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

int main(){
	int n;
	ll m; cin >> n >> m;
	vector<ll> a(n), b(n);
	rep(i,0,n) cin >> a[i];
	rep(i,0,n) cin >> b[i];

	rep(i,0,n){
		b[i] -= a[i];
		b[i] += m;
		b[i] %= m;
	}
	
	vector<ll> c(n+1);
	c[0] = b[0];
	rep(i,1,n){
		c[i] = b[i] - b[i-1];
	}
	c[n] = 0 - b[n-1];
	
	rep(i,0,n+1){
		c[i] += m;
		c[i] %= m;
	}
	
	sort(c.begin(), c.end());
	
	vector<ll> rui(n+2);
	rep(i,0,n+1){
		rui[i+1] += rui[i] + c[i];
	}
	
	if (rui[n+1] == 0){
		cout << 0 << '\n';
		return 0;
	}
	
	ll ans = 6e18;
	rep(i,0,n+1){
		if (rui[i] == m * (n+1 - i) - (rui[n+1] - rui[i])){
			chmin(ans, rui[i]);
		}
	}
	cout << ans << '\n';
}