#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#define rep(i, n) for(i = 0; i < n; i++)
using namespace std;

int n, m;
int a[200000];
int b[200000];

int main() {
	int i, j;
	
	cin >> n >> m;
	rep(i, n) cin >> a[i];
	rep(i, m) cin >> b[i];
	
	int minV = min(a[0], b[0]);
	int maxV = max(a[n - 1], b[m - 1]);
	int ans = maxV - minV;
	
	j = 0;
	rep(i, n - 1) {
		for (; j < m; j++) {
			if (b[j] >= a[i]) break;
		}
		
		vector<int> vec;
		vec.push_back(a[i]);
		for (; j < m; j++) {
			if (b[j] >= a[i + 1]) break;
			vec.push_back(b[j]);
		}
		vec.push_back(a[i + 1]);
		
		vector<int> sub;
		for (int k = 0; k + 1 < vec.size(); k++) {
			sub.push_back(vec[k + 1] - vec[k]);
		}
		sort(sub.begin(), sub.end(), greater<int>());
		ans -= sub[0];
	}
	
	cout << ans << endl;
	return 0;
}