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


using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
typedef pair<int, int> P;
int main()
{

    int n,k,i,a;
    long long s;

    s=0;
    fin>>n>>k;


    deque <P> q;

    for(i=1;i<=n;i++)
    {
        fin>>a;

        while(q.empty()==false && q.back().first>=a) q.pop_back();

        q.push_back(P(a,i));

        while(q.front().second<=i-k) q.pop_front();

       if(i>=k) s+=q.front().first;

    }

    fout<<s;

}