#include <fstream>

std::ifstream in("deque.in");
std::ofstream out("deque.out");

#define BUFFER_SIZE 1 << 17

int p; char buffer[BUFFER_SIZE];

__attribute__((always_inline)) int get_int()
{
    int number = 0; char sign = '+';

    while(buffer[p] < '0')
    {
        sign = buffer[p];

        if(++p == BUFFER_SIZE)
        {
           in.read(buffer, BUFFER_SIZE);

           p = 0;
        }
    }

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

        if(++p == BUFFER_SIZE)
        {
           in.read(buffer, BUFFER_SIZE);

           p = 0;
        }
    }

    if(sign == '-') number = -number;

    return number;
}

int v[5000001], deque[5000001];

int main()
{
    int N, K, front = 1, back = 0;

    long long sum = 0;

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

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

    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]];
    }

    out << sum;

    return 0;
}