#include <bits/stdc++.h>
using namespace std;
template <typename T>
T in() {
  char ch;
  T n = 0;
  bool ng = false;
  while (1) {
    ch = getchar();
    if (ch == '-') {
      ng = true;
      ch = getchar();
      break;
    }
    if (ch >= '0' && ch <= '9') break;
  }
  while (1) {
    n = n * 10 + (ch - '0');
    ch = getchar();
    if (ch < '0' || ch > '9') break;
  }
  return (ng ? -n : n);
}
template <typename T>
inline T Dist(T x1, T y1, T x2, T y2) {
  return sqrt((x1 - x2 * x1 - x2) + (y1 - y2 * y1 - y2));
}
template <typename T>
inline T POW(T B, T P) {
  if (P == 0) return 1;
  if (P & 1)
    return B * POW(B, P - 1);
  else
    return (POW(B, P / 2) * POW(B, P / 2));
}
template <typename T>
inline T ABS(T a) {
  if (a < 0)
    return -a;
  else
    return a;
}
template <typename T>
inline T Gcd(T a, T b) {
  if (a < 0) return Gcd(-a, b);
  if (b < 0) return Gcd(a, -b);
  return (b == 0) ? a : Gcd(b, a % b);
}
template <typename T>
inline T Lcm(T a, T b) {
  if (a < 0) return Lcm(-a, b);
  if (b < 0) return Lcm(a, -b);
  return a * (b / Gcd(a, b));
}
long long Bigmod(long long base, long long power, long long MOD) {
  long long ret = 1;
  while (power) {
    if (power & 1) ret = (ret * base) % MOD;
    base = (base * base) % MOD;
    power >>= 1;
  }
  return ret;
}
long long ModInverse(long long number, long long MOD) {
  return Bigmod(number, MOD - 2, MOD);
}
int Set(int N, int pos) { return N = N | (1 << pos); }
int Reset(int N, int pos) { return N = N & ~(1 << pos); }
bool Chkbit(int N, int pos) { return (bool)(N & (1 << pos)); }
bool isVowel(char ch) {
  ch = toupper(ch);
  if (ch == 'A' || ch == 'U' || ch == 'I' || ch == 'O' || ch == 'E')
    return true;
  return false;
}
bool isConst(char ch) {
  if (isalpha(ch) && !isVowel(ch)) return true;
  return false;
}
int toInt(string s) {
  int sm;
  stringstream ss(s);
  ss >> sm;
  return sm;
}
long long int toLlint(string s) {
  long long int sm;
  stringstream ss(s);
  ss >> sm;
  return sm;
}
template <typename T>
long long int isLeft(T a, T b, T c) {
  return (a.x - b.x) * (b.y - c.y) - (b.x - c.x) * (a.y - b.y);
}
long long int a[300005], b[300005];
int n, m;
int Check(long long int x) {
  int pos = 1;
  for (int i = 1; i <= n; i++) {
    if (pos <= m && b[pos] <= a[i] && (a[i] - b[pos]) > x) return 0;
    if (a[i] < b[pos]) {
      while (pos <= m && b[pos] - a[i] <= x) pos++;
    } else {
      int now = pos;
      pos++;
      while (pos <= m) {
        long long int p = (a[i] - b[now]) * 2LL + (-a[i] + b[pos]);
        long long int q = (a[i] - b[now]) + 2LL * (-a[i] + b[pos]);
        if (min(p, q) > x) break;
        pos++;
      }
    }
  }
  return (pos > m);
}
int main() {
  n = in<int>(), m = in<int>();
  int id = 0;
  for (int i = 1; i < n + 1; i++) {
    a[i] = in<long long int>();
  }
  for (int i = 1; i < m + 1; i++) {
    b[i] = in<long long int>();
  }
  long long int L = 0, R = 100000000000000, ans, mid;
  while (L <= R) {
    mid = (L + R) / 2LL;
    if (Check(mid)) {
      R = mid - 1LL;
      ans = mid;
    } else {
      L = mid + 1LL;
    }
  }
  cout << ans << endl;
  return 0;
}
