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

using namespace std;

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

const int NMAX=5000005;
int v[NMAX];
deque<int>dq;

int main()
{
    long long n,i,j,k,s=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    for(i=1;i<=n;i++)
    {
        if(!dq.empty() && dq.front()==i-k)
            dq.pop_front();
        while(!dq.empty() && v[dq.back()]>=v[i])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k)
            s=s+v[dq.front()];
    }
    fout <<s<< endl;
    return 0;
}