## Problem E. Elementary arithmetic ≡

• problems
 Author: A. Zhuplev, A. Klenin Time limit: 1 sec Input file: input.txt Memory limit: 256 Mb Output file: output.txt

### Statement

Underwater arithmetic is very elementary. There are just two operations: WITH and WITHOUT which mean addition and subtraction respectively.

Underwater mathematicians did not yet invent brackets, so all expressions are calculated from right to left. For example, the expression 3 WITH 5 WITHOUT 4 WITHOUT 7 is calculated as (3 + (5 − (4 − 7))).

Scientists of Nearsea Institute of Underwater Arithmetic need a program to evaluate such expressions.

### Input file format

First line of input file contains a single integer N. Following 2 × N + 1 lines describe the expression. Odd lines contain integer operands, even lines contain operations.

### Output file format

Output file must contain a single integer — calculation result.

### Constraints

1 ≤ N ≤ 103

All operands are in range from 0 to 103.

### Sample tests

No. Input file (input.txt) Output file (output.txt)
1
1
2
WITH
3
5
2
3
10
WITHOUT
5
WITH
3
WITH
15
-13

0.089s 0.015s 13