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#F2030. k-Tree

    ID: 2036 传统题 2000ms 256MiB 尝试: 0 已通过: 0 难度: 4 上传者: 标签>动态规划模拟树编程与模拟数据结构进阶难度共享题库Codeforces英文题面题目来源题面语言

k-Tree

题目描述

C. k-Tree
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Quite recently a creative student Lesha had a lecture on trees. After the lecture Lesha was inspired and came up with the tree of his own which he called a k-tree.

A k-tree is an infinite rooted tree where:

  • each vertex has exactly k children;
  • each edge has some weight;
  • if we look at the edges that goes from some vertex to its children (exactly k edges), then their weights will equal 1,2,3,...,k.

The picture below shows a part of a 3-tree.

As soon as Dima, a good friend of Lesha, found out about the tree, he immediately wondered: "How many paths of total weight n (the sum of all weights of the edges in the path) are there, starting from the root of a k-tree and also containing at least one edge of weight at least d?".

Help Dima find an answer to his question. As the number of ways can be rather large, print it modulo 1000000007 (109+7).

Input

A single line contains three space-separated integers: n, k and d (1≤n,k≤100; 1≤d≤k).

Output

Print a single integer − the answer to the problem modulo 1000000007 (109+7).

Examples
Input
3 3 2
Output
3
Input
3 3 3
Output
1
Input
4 3 2
Output
6
Input
4 5 2
Output
7

题目来源：fps-www.educg.net-codeforce-1-2833.xml.zip；FPS 共享题包，题包内第 1621 题。保留原作者与原赛事署名。