#include <iostream>
#include <deque>
#include <fstream>
using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

 int v[5000000];
int main()
{
    deque <int> D;
    int n,k,s=0;
    in>>n>>k;

    for(int i=0;i<n;i++)
        in>>v[i];
    D.push_front(0);
    for(int i=1;i<n;i++)
    {
        if(D.front()==i-k) D.pop_front();




        while(!D.empty() && v[i]<v[D.back()] )
            D.pop_back();
        D.push_back(i);
        if(i>=k-1) s+=v[D.front()];

    }
    cout<<s;
    return 0;
}