#include <iostream>
#include <fstream>

using namespace std;

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

long long s;
int i,n,k,v[5000010],a[5000010],prim,ultim;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
    }
    prim=1;
    ultim=0;
    for(i=1;i<=n;i++)
    {
        while(prim<=ultim and v[i]<=v[a[ultim]])
            ultim--;
        a[++ultim]=i;
        if(a[prim]==i-k)
            prim++;
        if(i>=k)
            s=s+v[a[prim]];
    }
    g<<s;
}