#include <iostream>
#include <fstream>
#include <deque>

using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
int main()
{
    long long n,k,i,a[5000100];
    deque<long long> d;
    long long s=0;
    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;
    f.close();
    g.close();
    return 0;
}