#include <iostream>
#include <fstream>

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

#define MaxN 5000010

int main()
{
    int n,k,i;
    int a[MaxN], Dque[MaxN];
    int Front, Back;
    long long sum=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>a[i];
    Front=1;Back=0;
    for (i=1;i<=n;i++)
    {
        while (Front<=Back && a[i]<=a[Dque[Back]])
            Back--;
        Dque[Back++]=a[i];
        if (Dque[Front]==i-k)
            Front++;
        if(i>=k)
          sum+=a[Dque[Front]];

    }
    g<<sum;
    f.close();
    g.close();
    return 0;
}