Print n! (n factorial): the product 1 × 2 × … × n. By definition 0! = 1.
Input
One integer 0 ≤ n ≤ 20.
Output
n! as an integer. Note that 20! does not fit in a 32-bit integer – use a 64-bit type in languages like C, C++ and Java (long long / long).
Read from standard input and write to standard output. 4 test cases in total (2 hidden). Tests for this language run inside your browser.