#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[5000005],deque[5000005];
long n,front,back,k,i;
long long s=0;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>a[i];
    front=1;
    back=0;
    for(i=1;i<=n;i++)
    {
        while(front<=back && a[i]<=a[deque[back]])
            back--;
        deque[++back]=i;
        if(deque[front]==i-k)
            front++;
        if(i>=k)
            s+=a[deque[front]];
    }
    g<<s;
    return 0;
}