The Parquet of the Triangles

prb47 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.

Specifications

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.

Problem information

Time Limit: 1 seconds
Memory Limit: 64 MB
Balls for the passed test: 6.66667
Complexity: 30% 85/122

Example

Example input

5 4
25 38

Example output

← The Segments

Problems

The Red and Blue Squares →