#include <stdio.h>
#include <ctype.h>

#define BUFFER_SIZE 1 << 17

char buffer[BUFFER_SIZE];

int p = BUFFER_SIZE;

inline char next()
{
    if(p == BUFFER_SIZE) fread(buffer, 1, BUFFER_SIZE, stdin), p = 0;

    return buffer[p++];
}

inline int get_int()
{
    int number = 0, sign = 1;

    char c = next();

    while(!isdigit(c) && c != '-') c = next();

    if(c == '-') c = next(), sign = -1;

    while(c > '/')

        number = number * 10 + c - 48, c = next();

    return number * sign;
}

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);

    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]];
    }

    printf("%lld", sum);

    return 0;
}