Author:  A. Zhuplev, A. Klenin  Time limit:  1 sec  
Input file:  input.txt  Memory limit:  256 Mb  
Output file:  output.txt 
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.
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 must contain a single integer — calculation result.
1 ≤ N ≤ 10^{3}
All operands are in range from 0 to 10^{3}.
No.  Input file (input.txt ) 
Output file (output.txt ) 

1 


2 

