## Problem E. Error detection ≡

 Author: I. Tuphanov Time limit: 1 sec Input file: input.txt Memory limit: 256 Mb Output file: output.txt

### Statement

FEFU computer scientists use a duplication method to detect errors in network data transfer. Each bit of data is duplicated. The duplicate follows the original bit. Each byte therefore is transferred as a message of two bytes. The first byte of the message encodes high bits of the original byte, the second byte encodes low bits.

For example, a byte 67 is encoded as follows:

1. 6710 = 010000112;
2. the sequence 01000011 is encoded as 0011000000001111;
3. the sequence 0011000000001111 is split into 00110000 and 00001111;
4. 001100002 = 4810, 000011112 = 1510, so the result is 48 15

Scientists received two bytes. Now they need to find out what the original byte was.

### Input file format

Input file contains two integers designating two received bytes.

### Output file format

Output file must contain a single integer — the original byte, or 1 if there was an error during transfer.

### Constraints

Both input integers are in the range from 0 to 255.

### Sample tests

No. Input file (input.txt) Output file (output.txt)
1
48 15

67

2
48 7

-1


0.102s 0.017s 15