2385.py

t,w = raw_input().split(" ")
T,W = int(t),int(w)

apple_data = []
for i in range(int(T)):
    apple_data.append(input()-1)


note= [[-1  for j in range(T) ] for i in range(W + 1)]


def Foo(area,cnt,state):
    on_get = 0
    if note[cnt][area] != -1:
        return note[cnt][area]

    if apple_data[area] == state:
        on_get = 1
    if (area == T-1):
        return on_get
    
    
    if (cnt == W):
        note[cnt][area] = Foo(area + 1,cnt,state) + on_get
    else:
        note[cnt][area] =  max(Foo(area+1,cnt,state) + on_get,Foo(area + 1,cnt + 1,state^1) + on_get)
    
    
    return note[cnt][area]

print max(Foo(0,0,0),Foo(0,1,1))