#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, k, v[5000001], d[5000001], x, minim, nr=0, front=1, back=0;
long long suma;
int main()
{
    f>>n>>k;
    for(int i=1; i<=n; i++)
        f>>v[i];
    for(int i=1; i<=n; i++)
    {
        while(front<=back && v[i]<=v[d[back]])
            back--;
        back++;
        d[back]=i;
        if(d[front]==i-k)
            front++;
        if(i>=k)
            suma=suma+v[d[front]];
    }
    g<<suma;
    f.close();
    g.close();
    return 0;
}