def solution(ar):
# 여기에 코드를 작성해주세요.
answer = 0
D = [[0]*3 for i in range(len(ar))]
D[0][1]=ar[0]
if len(ar) >1:
D[1][1]=ar[1]
D[1][2]=ar[0]+ar[1]
if len(ar) >2:
D[2][1] = ar[0]+ar[2]
D[2][2] = ar[1]+ar[2]
for i in range(3,len(ar)):
D[i][1] = max(D[i-2][2],D[i-2][1],D[i-3][1],D[i-3][2]) +ar[i]
D[i][2] = ar[i]+D[i-1][1]
M = 0
for i in range(len(ar)):
M = max(M,D[i][1],D[i][2])
return M
L =[]
for i in range(int(input())):
L.append(int(input()))
print(solution(L))