def solve(c,sm):
    global mn
    #print "c: ",c, "mn=",mn,"sm=",sm
    if len(c)-1<=2*k:
        return min(c)
    for i in range(min(len(c)-1,k+1)):
        s=sm+c[i]
        if k+i<=len(c)-1:
            s+=solve(c[i+k+1:],s)
        else:
            return s
        if s<mn:
            mn=s
        #print "s:",s
    return mn
        
n,k=map(int,raw_input().split())
c=map(int,raw_input().split())
mn=sum(c)

print solve(c,0)