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

            s+=a[d.front()];
        }
    }
    g<<s;
    return 0;
}