Recursion - 1#8609

Recursion - 1

1 second
128 megabytes
Very easy

Implement the recursive function:

f(n) = \begin{cases} 0, n = 0\\ f(n - 1) + n, n > 0 \end{cases}

Input

One integer n~(0 \le n \le 1000).

Output

Print the value of .

Examples

Example 1

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