n=int(input())
m=list(map(int,input().split()))
list1=[0]*n
list1[0]=m[0]
if n>2:

    list1[1]=max(list1[0],m[1])
    for i in range(n-2):
        list1[i+2]=max(list1[i]+m[i+2],list1[i+1])
    print(max(list1))

elif n==1:
    list1[0]=max(list1[0],m[0])
    print(list1[0])
elif n==2:
    list1[0]=max(list1[0],m[0])
    print(list1[0])