#include <stdio.h>

int N, K, v[5000001], deque[5000001], front = 1, back;

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]);
    }

    for(int i = 1; i <= N; i++)
    {
        while(front <= back && v[i] <= deque[back])
        {
            back--;
        }

        deque[++back] = v[i];

        if(deque[front] == v[i - K]) front++;

        if(i >= K) sum += deque[front];
    }

    printf("%lld", sum);

    return 0;
}