#include "bits/stdc++.h"
#define _CRT_SECURE_NO_WARNINGS
#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout << (p) << endl;
#define sP(p) cout << setprecision(15) << fixed << p << endl;
#define Pi pair<int,int>
#define IINF 1e9
#define LINF 1e18
#define vi vector<int>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
int dx[] = { 1, 0,-1,0 };
int dy[] = { 0, 1,0,-1 };

void solve() {
	int n, m;
	cin >> n >> m;
	vi pos;
	rep(i, m) {
		int a;
		cin >> a;
		pos.push_back(a);
	}
	int p = 0;
	int cost = 0;
	rep(i, n){
		int mini = 25252;
		int t;
		rep(j, pos.size()) {
			if (abs(p - pos[j]) < mini) {
				mini = abs(p - pos[j]);
				t = j;
			}
		}
		cost += mini;
		p = pos[t];
		pos.erase(pos.begin() + t);
	}
	P(cost);
}

int main() {
	solve();
	return 0;
}