N = int(input())
V = tuple(map(int, input().split()))
if N <= 2:
    print(max(V))
    exit()

dp = [[None] * 2 for i in range(N)]
dp[0][0] = 0
dp[0][1] = V[0]
dp[1][0] = V[0]
dp[1][1] = V[1]

for i in range(2, N):
    dp[i][0] = max(dp[i-1][1], dp[i-2][1])
    dp[i][1] = max(dp[i-1][0] + V[i], dp[i-2][0] + V[i])

print(max(dp[N-1][0], dp[N-1][1]))