#include <cstdio>

using namespace std;

int v[5000002], deq[5000002];

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    int n, k;
    scanf("%d%d", &n, &k);

    long long sol = 0;
    int left = 1, right = 0;
    for (int i = 1; i < k; i++)
    {
        scanf("%d", &v[i]);
        while (v[deq[right]] > v[i] && right > 0)
            right--;
        deq[++right] = i;
    }
    for (int i = k, x; i <= n; i++)
    {
        scanf("%d", &v[i]);
        while (v[deq[right]] > v[i] && right > left-1)
            right--;
        deq[++right] = i;
        if (i - deq[left] == k)
            left++;
        sol += v[deq[left]];
    }

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

    return 0;
}