# 2156 포도주 시식

n = int(input()) # 1<= n <= 10000

data=[0]
for i in range(n):
  data.append(int(input()))

many = [ 0 ]
many.append(data[1])
if n > 1 : 
  many.append(data[1]+data[2])

  for i in range(3,n+1):
    many.append( max(many[i-1],many[i-2]+data[i], many[i-3]+data[i-1]+data[i] ) )

print(many[n])