#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 < K; ++i)
    {
        while(front <= back && v[i] <= v[deque[back]])
        {
            --back;
        }

        deque[++back] = i;
    }


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

        deque[++back] = i;

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

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

    printf("%lld", sum);

    return 0;
}