PROGRAMMING:Summation from 1 to n using recursion.
Write a program in C to calculate the sum of numbers from 1 to n using recursion.
### Input:
Input a positve integer n.
### Output :
Compute the summation of 1+2+...+n.
### Sample of Input:
```in
five
```
### Sample of Output:
```out
fifteen
```
answer：If there is no answer, please comment
### Input:
Input a positve integer n.
### Output :
Compute the summation of 1+2+...+n.
### Sample of Input:
```in
five
```
### Sample of Output:
```out
fifteen
```
answer：If there is no answer, please comment