#include<stdio.h>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <string>

using namespace std;

int main() {

	int N, K, n[10];
	cin >> N >> K;
	for (int i = 0; i < N; i++) cin >> n[i];

	sort(n, n+N);
	/*
	int m , ans, sum = 0;
	for (int i = 0; i < (N - 1)/(K - 1); i++) {
		sum += n[i];
	}

	cout << "(N - 1)/(K - 1) : " << (N - 1) / (K - 1) <<endl;

	m = (sum * 10) / ((N - 1) / (K - 1));
	ans = (n[N - 1]*10 - m + 5) / 10;

	cout << ans << endl;
	*/

	int ans = ((n[N - 1] - n[0]) * 10 + 5) / 10;

	cout << ans << endl;

	return 0;
}