#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[5000002];
deque <int> dq;
int n,i,k;
long long sum=0;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
    }
    for(i=1;i<=n;i++)
    {
        while(!dq.empty()&&a[i]<=a[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front()==i-k)
            dq.pop_front();
        if(i>=k)
        {
            sum+=a[dq.front()];
        }
    }
    g<<sum;
    return 0;
}