#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int DY[]{1, 0, -1, 0}, DX[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1}, DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int solve(const vector<int>& a, int l) {
  const int n = a.size();
  if (n == 0) return 0;
  int ans = min(a.back(), l - a.front());
  FOR(i, 1, n) chmin(ans, a[i - 1] + l - a[i]);
  return ans;
}

int main() {
  int n, m; cin >> n >> m;
  vector<int> a(n), b(m);
  REP(i, n) cin >> a[i];
  REP(i, m) cin >> b[i];
  int ans = 0;
  if (b.back() > a.back()) {
    ans += b.back() - a.back();
    while (!b.empty() && b.back() > a.back()) b.pop_back();
  }
  reverse(ALL(a));
  reverse(ALL(b));
  if (!b.empty() && b.back() < a.back()) {
    ans += a.back() - b.back();
    while (!b.empty() && b.back() < a.back()) b.pop_back();
  }
  reverse(ALL(a));
  FOR(i, 1, n) {
    vector<int> c;
    while (!b.empty() && b.back() < a[i]) {
      c.emplace_back(b.back() - a[i - 1]);
      b.pop_back();
    }
    ans += solve(c, a[i] - a[i - 1]);
  }
  cout << ans << '\n';
  return 0;
}