#include <bits/stdc++.h>
#define NMAX 500005

using namespace std;
int n, k, v[NMAX], d[NMAX], st, dr;
long long sum;
int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    scanf("%d %d", &n, &k);
    for (int i = 1; i <= n; i++)
    {
        scanf("%d", &v[i]);
    }
    dr = 1;
    st = 0;
    for (int i = 1; i <= n; i++)
    {
        while (dr <= st && v[i] <= v[d[st]]) st--;
        d[++st] = i;
        if (d[dr] == i - k) dr++;
        if (i >= k) sum += v[d[dr]];
    }

    printf("%lld\n", sum);

    fclose(stdin);
    fclose(stdout);
    return 0;
}