#include <iostream>
#include <fstream>
#include <deque>
#define Nmax 5000005
#define ll long long

using namespace std;

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

int n, k;
int a[Nmax];
deque <int> dq;
ll sum;

int main()
{
    f >> n >> k;
    for (int i = 1; i <= n; i++) f >> a[i];

    for (int i = 1; i <= n; i++)
    {
        int x=a[i];
        while (!dq.empty() && x < a[dq.back()]) dq.pop_back();
        dq.push_back(i);
        if (dq.front()==i-k) dq.pop_front();
        if (i>=k) sum+=a[dq.front()];
    }
    g << sum;

    return 0;
}