package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
)

func main() {
	in := bufio.NewReader(os.Stdin)

	var n, m int
	fmt.Fscan(in, &n, &m)

	a := make([]int, m)
	for i := 0; i < m; i++ {
		fmt.Fscan(in, &a[i])
	}

	sort.Ints(a)

	ans := a[n-1] - a[0]
	for i := 1; i+n-1 < m; i++ {
		diff := a[i+n-1] - a[i]
		if diff < ans {
			ans = diff
		}
	}

	fmt.Println(ans)
}