Problems
Recursion - 1
Recursion - 1
Implement the recursive function:
f(n) = \begin{cases}
0, n = 0\\
f(n - 1) + n, n > 0
\end{cases}
Input data
One integer n~(0 \le n \le 1000).
Output data
Print the value of f(n).
Examples
Input example #1
5
Output example #1
15