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):
        A[i] = max(A[i-1],A[i-2]+sushi[i])
        
    print(A[N])