N = int(input())
V = [int(i) for i in input().split()]

dp = [[0, 0] for _ in range(N + 1)]
for i in range(1, N + 1):
    # 取らない
    dp[i][0] = max(dp[i-1])
    # 取る
    dp[i][1] = dp[i-1][0] + V[i-1]
ans = max(dp[N])
print(ans)