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