#include <iostream>
#include<fstream>
using namespace std;
long long q[5000000];
int deq[5000000];
int main()
{

    ifstream fin;
    fin.open("deque.in");
    ofstream gin;
    gin.open("deque.out");
    long long s = 0;
    int n,k;
    fin>>n>>k;
    int st=1,sf=0;
    for(int i=0;i<n;i++)
    {
        fin>>q[i];
        while(st <= sf && q[i]<=q[deq[sf]])
            sf--;
        sf++;
        deq[sf] = i;
        if(deq[st] < i-k+1)
            st++;
        if(i>=k-1)
        s = s + q[deq[st]];
    }
    gin<<s;

    return 0;
}