#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
void IOS() { ios::sync_with_stdio(0);cin.tie(0); }
 
typedef tree<pii,null_type,less<pii>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
 
ordered_set tr;
 
int main() {
    IOS();
    int n,k,a;
    cin>>n>>k;
    vector<pii>v;
    for(int i=0;i<n;i++){
        cin>>a;
        v.push_back({a,i});
    }
    for(int i=0;i<k-1;i++){
        tr.insert(v[i]);
    }
    ll ans = 0;
    for(int i=k-1;i<n;i++){
        tr.insert(v[i]);
        ans+=(*(tr.find_by_order((k-1)/2))).first;
        tr.erase(tr.find(v[i-k+1]));
    }
    cout<<ans<<'\n';
}

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MjIgNwo0IDMgOSA1IDMgNiAwIDIgOCA0IDcgOSAzIDggNSA3IDUgOSA4IDMgMSAxIA==

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