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

dp = [[0]*2 for _ in range(N)]
dp[0][1] = V[0]
for i in range(1, N):
    dp[i][0] = max(dp[i][0], dp[i-1][1], dp[i-1][0])
    dp[i][1] = max(dp[i][1], dp[i-1][0]+V[i])
print(max(dp[-1][0], dp[-1][1]))