N = int(input())
arr = list(map(int, input().split()))
dp = [[0]*2 for _ in range(N)]
dp[0][1] = arr[0]
for i in range(1,N):
    dp[i][0] = max(dp[i-1][1],dp[i-1][0])
    dp[i][1] = dp[i-1][0] + arr[i]
print(max(dp[-1]))