#include <iostream>
#include <fstream>
#include <vector>
#include <cstring>
#include <queue>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

#define pb push_back
#define ll long long
const int NMax = 5e6 + 5;
const int inf = 1e9 + 5;

int N,K;
int v[NMax];

struct elem {
    int idx,val;
    elem (int _idx = 0,int _val = 0) {
        idx = _idx;
        val = _val;
    }
};
bool operator <(elem a,elem b) {
    return a.val > b.val;
}

int main() {
    in>>N>>K;

    for (int i=1;i <= N;++i) {
        in>>v[i];
    }

    priority_queue<elem> Q;

    for (int i=1;i <= K;++i) {
        Q.push(elem(i,v[i]));
    }

    //cout<<Q.top().val<<'\n';
    ll sum = Q.top().val;
    for (int i=K+1;i <= N;++i) {
        Q.push(elem(i,v[i]));

        while (Q.top().idx < i-K+1) {
            Q.pop();
        }

        sum += Q.top().val;
        //cout<<Q.top().val<<'\n';
    }
    out<<sum<<'\n';

    in.close();out.close();
    return 0;
}