#include <cstdio>
#include <deque>
using namespace std;
deque <int> D;
int n,k,i,a[5000001];
long long suma;
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]);
    suma=0;
    for (i=1; i<=n; i++)
    {
        if (!D.empty())
        {
            if (D.front()+k-1<i) D.pop_front();
            while (!D.empty())
            {
                if (a[i]<=a[D.back()]) D.pop_back();
                else break;
            }
        }
        D.push_back(i);
        if (i>=k) suma+=1LL*a[D.front()];
    }
    printf("%lld\n",suma);
    return 0;
}