#include <iostream>
#include <cstdlib>
#include <vector>
#include <algorithm>
using namespace std;

int n,m;
vector<int> d(1000);

int pick(int now,int sum,int remain){
	remain-=1;
	int place;
	int tmp;
	int min=20000;
	for(int k=0;k<m;k++){
		if(d[k]!=10001){
			if(abs(d[k]-now)<=min){
				min=abs(d[k]-now);
				place=d[k];
				tmp=k;
			}
		}
	}
	sum+=min;
	now=place;
	d[tmp]=10001;
	if(remain==0)return sum;
	else pick(now,sum,remain);
}
int main(){
	cin>>n>>m;
	for(int i=0;i<m;i++)cin>>d[i];
	cout<<pick(0,0,n)<<endl;
}