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