#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;   }