#include<stdio.h>
#include<deque>
using namespace std;
struct mh
{
    int p,v;
};
deque <mh> d;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k,i,v;
    mh a;
    long long s;
    scanf("%d%d",&n,&k);
    for(i=1;i<=k;i++)
    {
        scanf("%d",&v);
        while(!d.empty())
        {
            if(v<=d.back().v)
                d.pop_back();
                else
                    break;
        }
        a.v=v;
        a.p=i;
        d.push_back(a);
    }
    s=d.front().v;
    for(i=k+1;i<=n;i++)
    {
        if(d.front().p==i-k)
        d.pop_front();
         scanf("%d",&v);
        while(!d.empty())
        {
            if(v<=d.back().v)
                d.pop_back();
                else
                    break;
        }
           a.v=v;
        a.p=i;
        d.push_back(a);
            s=s+d.front().v;
    }
    printf("%lld\n",s);
    return 0;
}