#include <cstdio>
#include <deque>
using namespace std;
int n, k, a[5000010];
long long sum;
deque < int > C;
int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    int i;
    scanf("%d %d ", &n, &k);
    for (i=1; i<=n; i++)   scanf("%d ", &a[i]);
    for (i=1; i<=n; i++)
    {
        while (C.size() && a[i]<=a[C.back()])
                C.pop_back();
        C.push_back(i);
        if (C.front()==i-k) C.pop_front();
        if (i>=k) sum+=a[C.front()];
    }
    printf("%lld\n", sum);
    return 0;
}