#include <algorithm>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <ostream>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#define INF 1000000000
#define rep(i,a,b) for (int i=(a);i<(b);i++)
#define rev(i,a,b) for (int i=(a)-1;i>=b;i--)
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef queue<int> qi;
typedef vector<int> vi;
typedef vector<string> vs;
int dx[4] = { 0, 1, 0, -1 };
int dy[4] = { 1, 0, -1, 0 };

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n, m;
	cin >> n >> m;
	vi d(m);
	rep(i,0,m) cin >> d[i];

	int now = 0;
	ll ans = 0;
	rep(i,0,n) {
		int x = abs(d[0]) - now;
		int z = 0;
		rep(j,0,d.size()) {
			int a = abs(d[j]) - now;
			if(x > a) {
				x = a;
				z = j;
			}
		}

		ans += x;
		now = d[z];
		d.erase(d.begin() + z, d.begin() + z + 1);
	}


	cout << ans << endl;

	return 0;
}