N=int(input())
V=list(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])