#include <fstream>
#include <deque>
#define NMAX 5000002
using namespace std;
ifstream  fin("deque.in");
ofstream fout("deque.out");
int N,K,v[NMAX];
long long ans;
deque<int> dq;

void citire()
{
    fin>>N>>K;

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

int main()
{
    citire();

    ans=0;
    for(int i=1; i<=N; i++)
    {
        while(!dq.empty() && v[i]<=v[dq.back()])
        {
            dq.pop_back();
        }

        dq.push_back(i);

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

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

    fout<< ans << "\n";

    return 0;
}