n = int(input())
sq = list(map(int,input().split()))

m1 = 0
m2 = 0
m3 = sq[0]
cnt = 1
while cnt < n:
    m4 = max([sq[cnt]+m2, sq[cnt]+m1])
    m1,m2,m3 = m2,m3,m4 
    cnt += 1

print(max([m1,m2,m3]))