<p>If <img alt="$S=1!+2!+3!+\cdots +99!$" height="14" src="https://latex.artofproblemsolving.com/0/9/d/09d3444cc5a421c483f8f275bd91d10cc3104387.png" width="210" />, then the units' digit in the value of S is:</p>