#include <iostream>
#include <deque>
#include <cstdio>
using namespace std;
deque <int> coada;
int n,k,mCit[5000001];
void citire()
{
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++)
        scanf("%d",&mCit[i]);
}
void stergere(int x)
{
    while(!coada.empty()&&mCit[coada.back()]>mCit[x])
        coada.pop_back();

}
long long solve()
{
    for(int i=1;i<k;i++)
    {
        stergere(i);
        coada.push_back(i);
    }
    long long s=0;
    for(int i=k;i<=n;i++)
    {
        stergere(i);
        coada.push_back(i);
        if(i-coada.front()==k)
            coada.pop_front();
        s+=mCit[coada.front()];
    }
    return s;
}
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    citire();
    printf("%lld",solve());
    return 0;
}