Aztec Treasure#4341
During recent excavations at Teotihuacan, archaeologists discovered a strange box, the contents of which were probably used during the legendary sacrifices held by Montezuma, along with many identical rectangular bone pieces of size 1 \times 2.
Archaeologists determined that, in order to open the box, one must tile its rectangular lid with these bone pieces in a certain way. The pieces cannot overlap or extend beyond the boundary of the lid. The archaeologists are afraid to damage the box, so they want to count all possible ways to tile the lid. Your task is to compute the number of such ways.
The only line contains two space-separated integers and , the length and the width of the box's lid (1 \le l, w \le 100).
Output the number of ways of tiling modulo 10^9 + 7.
Esempio 1