#include <iostream>
#include <fstream>
#include <deque>

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

int n,k,i,a[5000100];
deque<int> d;
long long s;
int main()
{

    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
        while(d.empty()==0 && a[i]<=a[d.back()])
            d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)
            d.pop_front();
        if(i>=k)
            s+=a[d.front()];
    }
    g<<s;
    f.close();
    g.close();
    return 0;
}