10321 - 阶乘

N的阶乘写作N!表示小于等于N的所有正整数的乘积。阶乘会很快的变大，如13!就必须用32位整数类型来存储，70！即使用浮点数也存不下了。你的任务 是找到阶乘最后面的非零位。举个例子,5!=12345=120所以5!的最后面的非零位是2，7！=1234567=5040，所 以最后面的非零位是4。

共一行，一个整数不大于4，220的整数N。

共一行，输出N!最后面的非零位。

The factorial of an integer N, written N!, is the product of all the integers from 1 through N inclusive. The factorial quickly becomes very large: 13! is too large to store in a 32-bit integer on most computers, and 70! is too large for most floating-point variables. Your task is to find the rightmost non-zero digit of n!. For example, 5! = 1 2 3 4 5 = 120, so the rightmost non-zero digit of 5! is 2. Likewise, 7! = 1 2 3 4 5 6 7 = 5040, so the rightmost non-zero digit of 7! is 4.

PROGRAM NAME: fact4 INPUT FORMAT A single positive integer N no larger than 4,220. SAMPLE INPUT (file fact4.in) 7

OUTPUT FORMAT A single line containing but a single digit: the right most non-zero digit of N! . SAMPLE OUTPUT (file fact4.out) 4