We saw the little game Marmot made for Mole’s lunch. Now it’s Marmot’s dinner time and, as we all know, Marmot eats flowers. At every dinner he eats some red and white flowers. Therefore a dinner can be represented as a sequence of several flowers, some of them white and some of them red.
But, for a dinner to be tasty, there is a rule: Marmot wants to eat white flowers only in groups of sizek.
Now Marmot wonders in how many ways he can eat betweenaandbflowers. As the number of ways could be very large, print it modulo1000000007(109+7).
，只能昏昏沉沉地沿着青草和泥土的气息前进。
