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

#define MAXSIZE 60

int comp_inc(const void *first, const void *second);

int main()
{
	int pieces[MAXSIZE];
	int n, m;
	scanf("%d%d", &n, &m);
	int i;
	for(i=0; i<m; ++i)
		scanf("%d", &pieces[i]);
	qsort(pieces, m, sizeof(pieces[0]), comp_inc);
	int min=1010;
	for(i=0; i<=(m-n); ++i)
	{
		if(pieces[i+n-1]-pieces[i]<min)
			min=pieces[i+n-1]-pieces[i];
	}
	printf("%d\n", min);
	return 0;
}

int comp_inc(const void *first, const void *second)
{
	return *(int *)first-*(int *)second;
}