import sys

def rec(i):
    if i > n - 1:
        return 0
    if i == n - 1:
        return a[i]
    if dp[i] != -1:
        return dp[i]
    
    mn = int(1e17)
    for j in xrange(i, min(i + k + 1, n)):
        mn = min(mn, a[j] + rec(j + k + 1))
    
    dp[i] = mn;
    return mn;

sys.setrecursionlimit(1000000)

n,k = map(int,raw_input().split())
a = map(int,raw_input().split())

dp = [-1 for i in range(n + 1)]

print(rec(0))