import linecache
f = open("deque.in", "r")
g = open("deque.out", "w")
n = int(f.readline(1))
o = int(f.readline(2))
a = 1
suma = 0
for j in range(2, n + 3 - o):
    min = int(linecache.getline("deque.in", j))
    for k in range(j + 1, j + o):
        if int(linecache.getline("deque.in", k)) < min:
            min = int(linecache.getline("deque.in", k))
    suma += min
g.write(str(suma))