#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000000
#define Inf64 1000000000000000001LL

int main(){
	
	int N,K;
	cin>>N>>K;
	vector<long long> a(N);
	rep(i,N){
		cin>>a[i];
	}
	long long ans = -Inf64*4;
	
	priority_queue<long long,vector<long long>,greater<long long>> Q;
	long long qs = 0;
	long long sum = 0;
	rep(i,N){
		sum += a[i];
		if(i!=0){
			Q.push(a[i] - sum);
			qs += a[i]-sum;
		}
		while(Q.size()>K-1){
			qs -= Q.top();
			Q.pop();
		}
		if(Q.size()==K-1)ans = max(ans,qs + sum * K);
	}
	cout<<ans<<endl;
	return 0;
}