#include <bits/stdc++.h>
#define Nmax 5000000

using namespace std;

int a[Nmax], n, k, q[Nmax];

int main()
{
    ifstream f("deque.in");
    f >> n >> k;
    for(int i = 1; i <= n; i++)
        f >> a[i];
    f.close();
    int front = 1;
    int back = 0;
    long long sum = 0;
    for(int i = 1; i <= n; i++)
    {
        while(front <= back && a[i] <= a[q[back]])
            back--;
        q[++back] = i;
        if(q[front] == i - k) front++;
        if(i >= k) sum += a[q[front]];
    }
    ofstream g("deque.out");
    g << sum << "\n";
    g.close();
    return 0;
}