The floor in Winnie the Pooh’s house is made of N row *M column square woods.
Today, Winnie wants to mop the floor.
Winnie is standing on the wooden floor in the upper right corner at the beginning, and his big belly can mop 1 or 2 adjacent pieces of wood at the same time.
Besides, Winnie is a lazy bear, so the next starting position must be adjacent to the last end one.
How many times does he need to clean the entire house at least?
In a single line you are given two integers N and M (1 ≤ N, M ≤ 24).
Output one number — how many times does he need to clean the entire house at least.