N = int(input())
sushi = list(map(int,input().split()))


if N == 1:
    print(sushi[0])
else:
    A = [0]*(N+1)
    A[1]=sushi[0]
    for i in range(2,N+1):
        A[i] = max(A[i-1],A[i-2]+sushi[i-1])
    
    print(A[N])