Problem link-https://www.codechef.com/TSCO2017/problems/TSECJ105/

Question- A teacher wants every student to work on a project. A student can work on a single project, either alone or with a partner (group of 2). The teacher is okay with any number of pairs or sole workers.

The teacher is curious to know that how many possible ways can N students form pairs or stay solo. Can you help?

Note: Since the answer can be large, print it modulo 10^9+7

Input:

2

2

3

Output:

2

4

My approach is use nc2(im getting WA),please explain your approach?