**Given an integer n, find the minimal k such that
k = m! (where m! = 1 * 2 * ... * m) for some integer m; k >= n. In other words, find the smallest factorial which is not less than n.**
For:
n = 17
the output should be:
leastFactorial(n) = 24
17 < 24 = 4! = 1 * 2 * 3 * 4, while 3! = 1 * 2 * 3 = 6 < 17)