#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[50000001],deq[50000001],k,n;
long long suma;
int main()
{
    f>>n>>k;
    int i,prim=1,ultim=0;
    for(i=1;i<=n;i++)
        f>>a[i];
    for(i=1;i<=n;i++)
    {
        while(a[i]<=a[deq[ultim]] && prim<=ultim)
                ultim--;
        ultim++;
        deq[ultim]=i;
        if(deq[prim]<=i-k)
                prim++;
        if(i>=k)
            suma+=a[deq[prim]];
    }
    g<<suma;

    return 0;
}