Water Volume

Alex has a glass that initially contains some quantity of water (it's possible that the glass is empty). He performs $N$ operations of two types:

1. Pour $x$ ml (millilitres) of water in the glass
2. Drink $x$ ml of water from the glass

Alex writes down on a piece of paper the initial quantity of water. After each operation he writes down another number, representing the new volume of water in the glass. In total there will be $N+1$ numbers.

You know that the lowest number written by Alex is $0$. Find the largest one.

Standard input

The first line contains a single integer $N$, the number of operations.

Each of the next $N$ lines contains two integers $t$ and $x$. If $t = 0$ Alex pours $x$ ml in the glass, if $t = 1$ he drinks $x$ ml.

Standard output

Print the answer, expressed in ml, on the first line.

Constraints and notes

• $1 \leq N \leq 1\,000$
• $1 \leq x_i \leq 1\,000$

4
0 1
0 1
0 1
1 3

3

2
1 15
1 24

39