#include <iostream>
#include <fstream>
using namespace std;

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

const int  N=5000001;

int d[N], v[N];

int main()
{
    int i, n, k, front=0, back=-1;
    long long s=0;
    //d reprezinta deque-ul
    fin>>n>>k;
    for(i=0; i<n; i++)
    {
        fin>>v[i];

        if(front <= back && d[front]==i-k)
        {
            ++front;
        }

        while(front<=back && v[i]<=v[d[back]])
        {
            --back;
        }

        d[++back]=i;

        if(i>=k-1)
        {
            s+=v[d[front]];
        }
    }

    fout<<s;
    return 0;

}