Factorial of N

Factorial of N

Compute N! using the classic recursive definition.

Input format

A single line with one integer N (0 <= N <= 20).

Output format

Print N! (the factorial of N). By definition 0! = 1.

Constraints

• Values fit in a 64-bit signed integer
• Trailing whitespace and a trailing newline are ignored by the judge

Read from stdin, write to stdout. Sample cases below show the exact format.

1

1

3

6