#include <iostream>
#include <fstream>
#define maxn 5000010

using namespace std;

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

int n, k;
int a[maxn], Deque[maxn];
int Front, Back;
long long sum;

int main()
{
    int i;
    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) sum += a[ Deque[Front]];
    }
    g<<sum;
    return 0;
}