ENG  RUSTimus Online Judge
Online Judge
Problems
Authors
Online contests
About Online Judge
Frequently asked questions
Site news
Webboard
Links
Problem set
Submit solution
Judge status
Guide
Register
Update your info
Authors ranklist
Current contest
Scheduled contests
Past contests
Rules

1638. Bookworm

Time limit: 1.0 second
Memory limit: 64 MB
Petya bought a 100-volume edition of Advice of Veterans of Programming Contests and hoped that the succession of his failures would come to an end. He mounted a bookshelf on the wall and put the volumes onto the shelf in increasing order from left to right closely to each other. But Petya didn't know that inside the first sheet of one of the volumes there lived a mathematical worm, which was infinitely small and very voracious. The worm started to gnaw its way through the volumes perpendicularly to the sheets. It stopped upon reaching the last sheet of another volume. The following day Petya discovered the damage and became interested in how many millimeters the worm had gnawed.

Input

The first line contains 4 positive integers not exceeding 100 and separated by a space: the thickness of each volume (without the covers taken into account), the thickness of each book-cover, the number of the volume from which the worm started its route, and the number of the volume where it stopped.

Output

Output the length of the worm's route.

Sample

inputoutput
10 1 1 2
2
Problem Author: Alex Samsonov
Problem Source: XIII Open USU Championship