#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <int> deq;
int a[5000005],n,k;
long long sum;
int main()
{
    f>>n>>k;sum=0;
    for(int i=1;i<=n;i++)
        f>>a[i];
    for(int i=1;i<=n;i++)
    {
        while(!deq.empty() && a[i]<=a[deq.back()])
        {
            deq.pop_back();
        }
        deq.push_back(i);
        if(deq.front()==i-k)
            deq.pop_front();
        if(i>=k)
            sum+=a[deq.front()];
    }
    g<<sum;
}