#include <stdio.h>

char *buffer = new char[45000000]; int p;

int get_int()
{
    int number = 0;

    char sign = '+';

    while(buffer[p] < 48)
    {
        sign = buffer[p];

        p++;
    }

    while(buffer[p] > 47)
    {
        number = number * 10 + buffer[p] - 48;

        p++;
    }

    if(sign == '+') return number;

    return -number;
}

int main()
{
    int N, K, v[5000001], deque[5000001], front = 1, back = 0;

    long long sum = 0;

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

    fread(buffer, 1, 45000000, stdin);

    N = get_int(); K = get_int();

    for(int i = 1; i <= N; i++)
    {
        v[i] = get_int();
    }

    delete buffer;

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

        deque[++back] = i;
    }


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

        deque[++back] = i;

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

        sum += v[deque[front]];
    }

    printf("%lld", sum);

    return 0;
}