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

dp = [float('inf') for i in xrange(n+ 1)]
dp[0] = 0

for i in xrange(1, n+1):
    dp[min(i+k, n)] = min(dp[min(i+k, n)], dp[max(i-k-1, 0)] + c[i-1])
#print dp
print dp[n]