#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using mint = atcoder::static_modint<998244353>;
// using mint = atcoder::static_modint<1000000007>;
using ld = long double;
using ll = long long;
#define mp(a,b) make_pair(a,b)
#define rep(i,s,n) for(int i=s; i<(int)n; i++)
const vector<int> dx{1,0,-1,0},dy{0,1,0,-1};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n,k;cin >> n >> k;
    vector<ll> a(n);rep(i,0,n)cin >> a[i];

    priority_queue<ll,vector<ll>,greater<ll>> Q;
    ll presum=0;
    ll ans=0;
    ll Qsum=0;
    {   
        ll s=0;
        for(int i=k-1; i>0; i--){
            s+=a[i];
            Q.push(s);
            ans+=s;
            Qsum+=s;
        }
        rep(i,0,k)presum+=a[i];
    }
    ans+=presum;

    ll w=0;
    rep(i,k,n){
        w+=a[i];
        Q.push(a[i]-w);
        Qsum+=a[i]-w;

        Qsum-=Q.top();Q.pop();
        presum+=a[i];
        ans=max(ans,presum+Qsum+w*(k-1));
    }
    cout << ans;
    
}