#include <bits/stdc++.h>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");
deque<int> x;
 int n,k,a[5000008],c;
 long long suma=0;
int main()
{

    in>>n>>k;
    for(int i =1;i<=n;i++)
        in>>a[i];
    c=k;
    k=1-k;
    for(int i =1;i<=n;i++)
    {
        while(!x.empty()&&a[i]<=a[x.back()])
            x.pop_back();

        while(x.empty()==false && x.front()<=k)
            x.pop_front();
        x.push_back(i);
        k++;

        if(i>=c)
            {
                suma+=a[x.front()];}

    }
    out<<suma;
    return 0;
}