#include <bits/stdc++.h>
#include <bits/stdc++.h>
#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/modint>
// using namespace atcoder;
// using mint = modint998244353;
using ll = long long;
#define fix(x) fixed << setprecision(x)
#define rep(i, n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,k;
    cin >> n >> k;
    vector<ll> a(n), tot(n+1,0);
    rep(i,n) cin >> a[i];
    rep(i,n) tot[n-i-1] = tot[n-i] + a[n-i-1];
    ll ans, x = tot[0];
    priority_queue<ll, vector<ll>, greater<ll>> pq;
    for(int i=1;i<k;++i) pq.emplace(tot[i]), x += tot[i];
    ans = x - tot[k] * k;
    for(int i=k;i<n;++i){
        x += tot[i];
        pq.emplace(tot[i]);
        x -= pq.top();
        pq.pop();
        chmax(ans, x - tot[i+1] * k);
    }
    cout << ans << '\n';
    return 0;
}