Package for this problem was not updated by the problem writer or Codeforces administration after we’ve upgraded the judging servers. To adjust the time limit constraint, solution execution time will be multiplied by 2. For example, if your solution works for 400 ms on judging servers, than value 800 ms will be displayed and used to determine the verdict.

Virtual contest is a way to take part in past contest, as close as possible to participation on time. It is supported only ACM-ICPC mode for virtual contests.
If you've seen these problems, a virtual contest is not for you - solve these problems in the archive.
If you just want to solve some problem from a contest, a virtual contest is not for you - solve this problem in the archive.
Never use someone else's code, read the tutorials or communicate this other person during a virtual contest.

No tag edit access

A. Tiling with Hexagons

time limit per test

2 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputSeveral ages ago Berland was a kingdom. The King of Berland adored math. That's why, when he first visited one of his many palaces, he first of all paid attention to the floor in one hall. The floor was tiled with hexagonal tiles.

The hall also turned out hexagonal in its shape. The King walked along the perimeter of the hall and concluded that each of the six sides has *a*, *b*, *c*, *a*, *b* and *c* adjacent tiles, correspondingly.

To better visualize the situation, look at the picture showing a similar hexagon for *a* = 2, *b* = 3 and *c* = 4.

According to the legend, as the King of Berland obtained the values *a*, *b* and *c*, he almost immediately calculated the total number of tiles on the hall floor. Can you do the same?

Input

The first line contains three integers: *a*, *b* and *c* (2 ≤ *a*, *b*, *c* ≤ 1000).

Output

Print a single number — the total number of tiles on the hall floor.

Sample test(s)

Input

2 3 4

Output

18

Codeforces (c) Copyright 2010-2015 Mike Mirzayanov

The only programming contests Web 2.0 platform

Server time: 2015-06-30 08:14:30 (c3).