#include <bits/stdc++.h>
#define maxn 5000010

#define in "deque.in"
#define out "deque.out"
using namespace std;
ifstream fin(in);
ofstream fout(out);

int n,k;
int a[maxn], q[maxn];
int Front, Back;
int64_t sum;

int main()
{
    int i;

    fin >> n >> k;

    for (i = 1; i <= n; i++)
        fin >> a[i];

    Front = 1, Back = 0;

    for (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]];
    }

    fout << sum << "\n";

    fin.close();
    fout.close();
    return 0;
}