f = open("deque.in")
N, K = f.readline().split()
N = int(N)
K = int(K)
L = [0] * 5000001
Deque = [0] * 5000001
s = 0
for i in range(N):
    L[i] = int(f.readline())
start = 0
capat = -1
for i in range(N):
    while start <= capat and L[i] <= L[Deque[capat]]:
        capat -= 1
    capat += 1
    Deque[capat] = i
    if Deque[start] == i - K:
        start += 1
    if i + 1 >= K:
        s += L[Deque[start]]
g = open("deque.out", 'w')
g.write(str(s))