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Problems

Dominoes

Dominoes

Time limit 1 second
Memory limit 128 MiB

Given a rectangular board m × n. Find the number of ways to pave her dominoes - rectangles of size 1 × 2 cell.

prb628

Input data

Two numbers m and n (1m, n10) are given on a line.

Output data

Print the number of ways to pave the board with dominoes of given size.

Examples

Input example #1
1 1
Output example #1
0
Input example #2
2 3
Output example #2
3