How to calculate factorial of larger integer numbers ( i.e. numbers greater than 20 ) using C/C++ using high precision arithmetic ?

Here is my submission 4089042 for the problem 328A - IQ Test... It received "Judgement Failed" on last test case...The solution seems okay to me but can't understand why judgement had been failed... Can you suggest something guys?????

Here is my solution 3420156 for the problem 283A - Cows and Sequence... Logically it is giving correct solution but time limit gets exceeded on test no. 37.Can you help me in faster way of doing it?