#include<stdio.h>
#include<stdlib.h>

#define MIN(a,b) ((a)<(b)?(a):(b))

void sort(int *a,int n){
  if(n<=1) return;

  int pivot=a[0];
  int l=1;
  int r=n-1;
  while(l<=r){
    if(pivot>=a[l]){
      a[l-1]=a[l];
      l++;
    } else {
      int t=a[r];
      a[r]=a[l];
      a[l]=t;
      r--;
    }
  }
  a[r]=pivot;
  sort(a,r);
  sort(a+r+1,n-r-1);
}

void run(void){
  int n,m;
  scanf("%d%d",&n,&m);
  int *d=(int *)malloc(sizeof(int)*m);
  int i;
  for(i=0;i<m;i++){
    scanf("%d",d+i);
  }
  sort(d,m);

  int ans=100000;

  for(i=0;i<m-n+1;i++){
    if(d[i+n-1]<=0){
      ans=MIN(ans,-d[i]);
    } else if(d[i]<0){
      ans=MIN(ans,MIN(-2*d[i]+d[i+n-1],2*d[i+n-1]-d[i]));
    } else {
      ans=MIN(ans,d[i+n-1]);
    }
  }
  printf("%d\n",ans);
  free(d);
  return;
}

int main(void){
  run();
  return 0;
}