n=int(input())
v=[*map(int,input().split())]
if n==1:
    print(v[0])
else:
    a=[0]*(n+1)
    a[1]=v[0]
    for i in range(2,n+1):
        a[i]=max(a[i-1],a[i-2]+v[i-1])
    print(a[n])