#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, M;
  cin >> N >> M;
  vector<int> A(N);
  for (int i = 0; i < N; i++){
    cin >> A[i];
  }
  vector<int> B(N);
  for (int i = 0; i < N; i++){
    cin >> B[i];
  }
  vector<int> D(N + 2);
  D[0] = 0;
  D[N + 1] = 0;
  for (int i = 0; i < N; i++){
    D[i + 1] = (B[i] - A[i] + M) % M;
  }
  vector<int> DD(N + 1);
  for (int i = 0; i <= N; i++){
    DD[i] = (D[i + 1] - D[i] + M) % M;
  }
  long long sum = 0;
  for (int i = 0; i <= N; i++){
    sum += DD[i];
  }
  int cnt = sum / M;
  sort(DD.begin(), DD.end(), greater<int>());
  for (int i = 0; i < cnt; i++){
    DD[i] -= M;
  }
  long long ans = 0;
  for (int i = 0; i <= N; i++){
    ans += abs(DD[i]);
  }
  cout << ans / 2 << endl;
}