#include <stdio.h>

#define maxn 5000010

int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;

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]);
    Front=1,
    Back=0;
    for (i=1; i<=N; i++)
    {
        while (Front<=Back && A[i]<=A[Deque[Back]])
            Back--;
        Deque[++Back]=i;
        if (Deque[Front]==i-K)
            Front++;
        if (i>=K)
            Sum+=A[Deque[Front]];
    }

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

    return 0;
}