#include<stdio.h>
#include <iostream>
#include <fstream>
int f,b,n,i,k;
long long rez=0;
int a[5000001],deq[5000001];

std::ifstream in("deque.in");
std::ofstream out("deque.out");
int main()
{
    in>>n>>k;
    for(i=1;i<=n;i++)
        in>>a[i];
    f=1;
    b=0;
    for(i=1;i<=n;i++)
    {
        while(f<=b && a[i]<=a[deq[b]])
            b--;
        deq[++b]=i;
        if(deq[f]==i-k)
            f++;
        if(i>=k)
            rez+=a[deq[f]];
    }
    out<<rez;
    return 0;
}