/*
TASK: seq
LANG: C++
*/
#include <iostream>

using namespace std;

#define _MAX 1000000

int n;
int k;
long long int r;
int a[_MAX];

void init()
{
	cin >> n;
	cin >> k;
	for (int i = 0 ; i < n; i++)
		cin >> a[i];
}

void solve()
{
	long long int factoriel = 1;
	long long int k_factoriel = 1;
	
	for (int i = 2; i <= k; i++)
		k_factoriel *= i;
	for (int i = n - 1; i > n - k - 1; i--)
	{
		factoriel *= i;
		if (factoriel > 1 && k_factoriel > 1)
		{
			int j = 10;
			while (j > 1)
			{
				while (factoriel % j == 0 && k_factoriel % j == 0)
				{
					factoriel /= j;
					k_factoriel /= j;
				}
				j--;
			}
		}
	}
	for (int i = 0; i < n; i++)
		r += (a[i] * factoriel);
	
	cout << r << endl;
}

int main()
{
	init();
	solve();
	
    return 0;
}
