#include <bits/stdc++.h>

using namespace std;

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

int n,i,k,f=1,b=0; // f=front,b=back, f>b=deque vid
int a[5000010],d[5000010];
long long S; //suma

int main()
{
    in>>n>>k;
    for(i=1; i<=n; i++)
        in>>a[i]; //citim sirul dat
    for(i=1; i<=n; i++)
    {
        while (f<=b && a[i]<=a[d[b]])
            b--;
        d[++b] = i;  // Adaugam pozitia elementului curent in deque
        if (d[f] == i-k) f++;
        if (i >= k)
            S+=a[d[f]];
    }
    out<<S;

    return 0;
}