#include<iostream>
#include<cstdio>
#include<algorithm>
#define LL long long
using namespace std;

const int maxn = 1e5 + 10;
int n, k;
int a[maxn];
int mul[maxn];
LL line[maxn];
LL pre[maxn];
LL ans = 1e18;

int read();

int main() {
	freopen("qwa.in", "r", stdin);
	freopen("qwa.out", "w", stdout);
	int i, j;
	n = read(); k = read();
	for(i = 1; i <= k - 1 - 2; i++)
		mul[i] = (k - 2 - i)*i;
	for(i = 1; i <= n; i++)
		a[i] = read();
	sort(a + 1, a + n + 1);
	for(i = 2; i <= n; i++) {
		line[i - 1] = a[i] - a[i - 1];
		pre[i - 1] = pre[i - 2] + line[i - 1];
	}
	if(k == 2) {
		for(i = 1; i <= n - 1; i++)
			ans = min(ans, line[i]);
		cout << ans << "\n";
		return 0;
	}
	if(k == 3) {
		for(i = 2; i <= n - 1; i++) 
			ans = min(line[i] + line[i - 1], ans);
		cout << (ans << 1) << "\n";
		return 0;
	}
	for(i = 1; i + k - 1 <= n; i++) {
		LL tmp = (pre[i + k - 2] - pre[i - 1])*(k - 1);
		int cnt = 1;
		for(j = i + 1; j <= i + k - 3; j++)
			tmp += line[i]*mul[cnt++];
		ans = min(tmp, ans);
	}
	cout << ans << "\n";
	return 0;
}

int read() {
	char s = getchar();
	int f = 1, t = 0;
	while(s < '0' || s > '9') {
		if(s == '-')
			f = -1;
		s = getchar();
	}
	while(s >= '0' && s <= '9') {
		t = (t << 3) + (t << 1) + s - '0';
		s = getchar();
	}
	return t*f;
}