N = int(input())
a = list(map(int, input().split()))
#print(a)
dp =[0 for i in range(N)]
dp[0] = a[0]
#print(dp)

if N >= 3:
    dp[1] = max(dp[0],a[1])
    for i in range(2,N):
        dp[i] = max(dp[i-2]+a[i],dp[i-1])
        
    print(max(dp))

elif N == 2:
    dp[1] = max(a[0], a[1])
    print(dp[N])

elif N == 1:
    dp[0] = a[0]
    print(dp[0])