#include <iostream>
#include <fstream>

using namespace std;

int a[500001], dcoad[500001];

int main()
{
    int n,k,i,st,dr;
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    fin>>n>>k;
    for (int i=0;i<n;i++)
        fin>>a[i];
    st=1;
    dr=0;
    for (int i=0;i<n;i++)
    {
        while (dr>=st&&dcoad[dr]>a[i])
            dr--;
        dcoad[++dr]=i;
        if(dcoad[st]==i-k)st++;
        if (i>=k-1)
            sum+=a[dcoad[st]];
    }
    fout<<sum;
    return 0;
}