#include<fstream>
#include<deque>
#define _NM 5000010
using namespace std;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int nA,k; static int A[_NM];
    fin>>nA>>k;
    deque<int> i_dq;
    long long sum=0;
    for (int i=1;i<=nA;i++)
    {
        fin>>A[i];
        if (i_dq.front()==i-k) i_dq.pop_front();
        while (!i_dq.empty()&&A[i_dq.back()]>=A[i]) i_dq.pop_back();
        i_dq.push_back(i);
        if (i>=k) sum+=A[i_dq.front()];
    }
    fout<<sum;
    return 0;
}