def chmax(DP,i,v):
    if DP[i] < v: DP[i] = v

N = int(input())
V = list(map(int, input().split()))
dp = [[-1] * (2) for _ in range(N + 1)]
dp[0][0] = 0
for i in range(N):
    for j in range(2):
        if dp[i][j] == -1:
            continue
        # j == 0 ... 取ってない ... 0,1
        # j == 1 ... 取ってる ... 0 のみ
        chmax(dp[i + 1], 0, dp[i][j])
        if j == 0:
            chmax(dp[i + 1], 1, dp[i][j] + V[i])
print(max(dp[-1]))