Problems

# The Parquet of the Triangles

# The Parquet of the Triangles

We laid by three-cornered tiles the rectangular room with sides **M** to **N** (at first for hori-zontal lines, and then for vertical lines) and we numbered it as shown on the picture.

It is possible to move from one parquet to another through a general side only for one step. Find the least quantity of steps, which necessary for transferring from parquet **A** to parquet **B**.

**Input **

In the input file in the first line through the gap is set to **M**, **N **(**1** ≤ **M**, **N** ≤ **100**), and the second - **A**, **B**.**Output **

The desired number of steps.

Input example #1

5 4 25 38

Output example #1

5