#include <iostream>
#include <cstdio>
using namespace std;

int n,k;
long long int s;
int a[5000001];

class Deque
{
private:
    int inc,sf;
    long long int arr[50000001];
public:
    Deque()
    {
        inc=sf=0;
    }
    void adauga_inceput(int x)
    {
        for(int i=inc;i<=sf+1;i++)
            arr[i+1]=arr[i];
        sf++;
        arr[++inc]=x;
    }
    void adauga_sfarsit(int x)
    {
        arr[++sf]=x;
    }
    int prim()
    {
        return arr[inc];
    }
    int ultim()
    {
        return arr[sf];
    }
    void scoate_prim()
    {
        inc++;
    }
    void scoate_ultim()
    {
        sf--;
    }
    bool vida()
    {
        return inc==sf;
    }
};

Deque d;

void solve()
{
    scanf("%d %d",&n,&k);

    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);

    for(int i=1;i<k ;i++)
    {
        while(!d.vida() && a[d.ultim()]>=a[i])
            d.scoate_ultim();
        d.adauga_sfarsit(i);
    }

    for(int i=k;i<=n;i++)
    {
        if(!d.vida() && d.prim()<=i-k)
                d.scoate_prim();
        while(!d.vida() && a[d.ultim()]>=a[i])
                d.scoate_ultim();
            d.adauga_sfarsit(i);
        s+=a[d.prim()];
    }
    printf("%lld",s);
}

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    solve();
    return 0;
}