#!/usr/bin/env python3

import sys
from collections import deque

sys.stdout = open('deque.out', 'w')

with open('deque.in', 'r') as f:
    d = deque()

    N, K = tuple(map(int, f.readline().split()))
    s = 0
    for i in range(N):
        x = int(f.readline()), i
        if d and i - d[0][1] >= K:
            d.popleft()
        while d and x[0] <= d[-1][0]:
            d.pop()

        d.append(x)
        if i >= K - 1:
            s += d[0][0]

    print(s)