#include <fstream>
#include <deque>

#define DIM 5000005

using namespace std;

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

deque<int>deq;

int N, K;
int A[DIM];
long long ans;


int main()
{
    fin >> N >> K;

    for(int i = 1; i <= N; i ++)
    {
        fin >> A[i];
    }

    for(int i = 1; i <= N; i ++)
    {
        while(!deq.empty() && A[i] <= A[ deq.back() ])
        {
            deq.pop_back();
        }
        deq.push_back(i);

        if(deq.front() == i - K)
        {
            deq.pop_front();
        }

        if(i >= K)
        {
            ans += A[ deq.front() ];
        }
    }

    fout << ans;


    return 0;
}