#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;

using S = pair<ll,int>;
S op(S lhs, S rhs){return max(lhs, rhs);}
constexpr S e(){return make_pair(-(1ll << 62), -1);}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll n, k;
    cin >> n >> k;
    vector<ll> a(n);
    for(auto &&v : a) cin >> v;
    ll sv = 0, mx = -(1ll << 62);
    int p = 0;
    for(int i = 0; i < n; i++){
        sv += a[i];
        if(i >= k - 1 && sv > mx){
            mx = sv;
            p = i + 1;
        }
    }
    vector<pair<ll,int>> sv2(n + 1);
    sv2[n] = make_pair(0, n);
    for(int i = n - 1; i >= 0; i--){
        sv2[i] = make_pair(sv2[i + 1].first + a[i], i);
    }
    atcoder::segtree<S, op, e> seg(sv2);
    ll ans = mx;
    int l = 1;
    for(int i = k - 2; i >= 0; i--){
        int r = p - i;
        auto pa = seg.prod(l, r);
        ans += pa.first - sv2[p].first;
        l = pa.second + 1;
    }
    cout << ans << '\n';
}