N = int(input())
V = list(map(int, input().split()))
dp = [[0 for _ in range(2)] for _ in range(N+1)]

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

print(max(dp[N]))