// #include <bits/allocator.h> // Temp fix for gcc13 global pragma
// #pragma GCC target("avx2,bmi2,popcnt,lzcnt")
// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
#if __cplusplus >= 202002L
using namespace numbers;
#endif
#ifdef LOCAL
	#include "Debug.h"
#else
	#define debug_endl() 42
	#define debug(...) 42
	#define debug2(...) 42
	#define debugbin(...) 42
#endif



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	int n, k;
	cin >> n >> k;
	vector<long long> pref(n + 1);
	for(auto i = 0; i < n; ++ i){
		cin >> pref[i + 1];
		pref[i + 1] += pref[i];
	}
	multiset<long long, greater<>> s;
	long long sum = 0;
	for(auto i = 1; i < k; ++ i){
		s.insert(pref[i]);
		sum += pref[i];
	}
	long long res = numeric_limits<long long>::min() / 2;
	for(auto i = k; i <= n; ++ i){
		res = max(res, pref[i] * k - sum);
		s.insert(pref[i]);
		sum += pref[i] - *s.begin();
		s.erase(s.begin());
	}
	cout << res << "\n";
	return 0;
}

/*

*/