/**
	author:  shobonvip
	created: 2025.03.07 21:17:18
**/

#include<bits/stdc++.h>
using namespace std;

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)
#define all(v) v.begin(), v.end()

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	
	ll n, k; cin >> n >> k;
	vector<ll> a(n);
	rep(i,0,n) cin >> a[i];
	vector<ll> rui(n + 1);
	rep(i,0,n) {
		rui[i+1] = a[i];
	}
	//cout << rui[0] << endl;
	rep(i,0,n) {
		rui[i+1] += rui[i];
		//cout << rui[i+1] << endl;
	}

	priority_queue<ll> pq;
	ll tmp = 0;
	ll ans = -5e18;
	rep(i,0,n) {
		if (i == 0) {
			tmp += rui[0];
		}else {
			tmp += rui[i];
			pq.push(rui[i]);
			if ((int)pq.size() > k-1) {
				//cout << pq.top() << ' ' << "DEL" << endl;
				tmp -= pq.top();
				pq.pop();
			}
		}
		if ((int)pq.size() == k-1) {
			//cout << rui[i+1] << ' ' << tmp << endl;
			chmax(ans, rui[i+1] * k - tmp);
		}
	}
	cout << ans << endl;
}