#include <cstdio>

using namespace std;
int i,b[5000004],a[5000004],u,p,n,k;
long long s;
void pune (int i)
{
    while (u>=p && a[b[u]]>a[i])
    {
        b[u]=0;
        u--;
    }
    u++;
    b[u]=i;
}
int main()
{
    freopen ("deque.in","r",stdin);
    freopen ("deque.out","w",stdout);
    scanf ("%d %d",&n,&k);
    for(i=1; i<=n; i++)
    scanf ("%d",&a[i]);
    u=0;
    p=1;
    for(i=1; i<k; i++)
        pune(i);
    for(i=k; i<=n; i++)
    {
        pune(i);
        s+=a[b[p]];
        if(i-b[p]==k-1)
        {
            b[p]=0;
            p++;
        }
    }
    printf ("%lld",s);
    return 0;
}