#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (ll i=(ll)from; i<(ll)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (ll i=(ll)N-1; i>=0; i--)
#define popcount __builtin_popcount

const ll LLINF = pow(2,61)-1;
const ll INF = pow(2,30)-1;

ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }

int main() {
  ll N, M; cin >> N >> M;
  vector<ll> A(N); rep(i,N) cin >> A[i];
  vector<ll> B(M); rep(i,M) cin >> B[i];

  assert(1<=N && N<=200000);
  assert(1<=M && M<=200000);
  rep(i,N) assert(1<=A[i] && A[i]<=1000000000 && (i==0||A[i-1]<A[i]));
  rep(i,M) assert(1<=B[i] && B[i]<=1000000000 && (i==0||B[i-1]<B[i]));
  set<ll> s; rep(i,N) s.insert(A[i]); rep(i,M) s.insert(B[i]);
  assert(s.size()==N+M);

  vector<p_ll> v;
  v.push_back(make_pair(-1*LLINF, 0));
  v.push_back(make_pair(LLINF, 0));
  rep(i,N) v.push_back(make_pair(A[i],0));
  rep(i,M) v.push_back(make_pair(B[i],1));
  sort(all(v));

  ll result = 2*LLINF+1 - (N+2), m = 0;
  rep(i,N+M+1) {
    m = max(m, v[i+1].first-v[i].first-1);
    if (v[i+1].second==0) {
      result -= m;
      m = 0;
    }
  }
  cout << result << endl;
  return 0;
}