#include <bits/stdc++.h>
 
using namespace std;

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

int main()
{
    int n, k, front = 0, back = -1;
    long long sum = 0;
 
    f >> n >> k;
    int v[n+1], deq[n];
 
    for (int i = 0; i < n; i++)
        f >> v[i];
    f.close();
 
    for (int i = 0; i < n; i ++)
    {
        while (front <= back && v[i] < v[deq[back]])
            back--;
        back++;
        deq[back] = i;
        if (deq[front] == i-k)
            front++;
        if (i >= k-1)
            sum += v[deq[front]];
 
    }
 
    g<< sum;
    g.close();
    return 0;
 
}