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

dp = [[0, 0] for _ in range(N+1)]

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