#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> dq;
int n,k,a[500001],s;
int main()
{
    fin>>n>>k;
    for (int i=1;i<=n;i++)
    {
        fin>>a[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) s+=a[dq.front()];
    }
    fout<<s;
    return 0;
}