Given is a number sequence $A_1, A_2, A_3, \dots, A_N$, which may contain negative elements.  
On a number line, there is a robot at coordinate $0$. It will do the following actions in order:

-   Move $A_1$ in the positive direction.
-   Move $A_1$ in the positive direction, and then move $A_2$ in the positive direction.
-   Move $A_1$ in the positive direction, then move $A_2$ in the positive direction, and then move $A_3$ in the positive direction.

$\hspace{140pt} \vdots$

-   Move $A_1$ in the positive direction, then move $A_2$ in the positive direction, then move $A_3$ in the positive direction, $\ldots$, $\dots$, and then move $A_N$ in the positive direction.

Find the greatest coordinate occupied by the robot from the beginning to the end of the process.

Input is given from Standard Input in the following format:

```
$N$
$A_1 \hspace{7pt} A_2 \hspace{7pt} A_3 \hspace{5pt} \dots \hspace{5pt} A_N$
```

Print the greatest coordinate occupied by the robot from the beginning to the end of the process.

-   $1 \le N \le 200000$
-   $-10^8 \le A_i \le 10^8$
-   All values in input are integers.

5

The robot moves as follows:

• Move 2 in the positive direction, to coordinate 2.
• Move 2 in the positive direction, to coordinate 4. Then move −1 in the positive direction, to coordinate 3.
• Move 2 in the positive direction, to coordinate 5. Then move −1 in the positive direction, to coordinate 4. Then move −2 in the positive direction, to coordinate 2.

The greatest coordinate occupied during the process is 5, so we should print 5.

0

In this case, the initial coordinate 0 is the greatest coordinate occupied.