n=int(input())
v=[int(i) for i in input().split()]
if 1<len(v):
    for i in range(0,n):
        d.append([])
    d[0]=v[0]
    d[1]=max(v[0],v[1])

    for i in range(2,n):
        d[i]=max(d[i-1],d[i-2]+v[i])

    ans=d.pop()
    print(ans)
else:
    print(v[0])