#include <iostream>
#include <fstream>

using namespace std;

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

int v[5000010], aux[5000010]={0};

int main()
{   int n,k,s=0,i,sfarsit=-1,start=0;
    in>>n>>k;
    for(i=0; i<n; i++){
        in>>v[i];
        while(start<=sfarsit && v[i]<=v[aux[sfarsit]]){
            sfarsit--;
        }
        sfarsit++;
        aux[sfarsit]=i;
        if(aux[start]==i-k && i>=k) start++;

        if(i>=k-1)
            s=s+v[aux[start]];

    }
    out<<s;
    in.close();
    out.close();
    return 0;
}