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

N = int(input())
V = list(map(int, input().split()))
DP = [[0] * (2) for _ in range(N + 1)]
for i in range(N):
    for j in range(2):
        if j == 1:
            chmax(DP[i + 1], 0, DP[i][j] + V[i])
        # 共通
        chmax(DP[i + 1], 1, DP[i][j])

ans = max(DP[-1])
print(ans)