IF ELSE condition in SharePoint calculated column?

Question

<h3 itemprop="name" style=" relative; font-weight: normal; normal; font-size: 18px; font-family: Arial, Tahoma, Helvetica, FreeSans, sans-serif; background-color: #ffffff;">How to add IF ELSE statement in calculated columns of SharePoint 2013</h3><div style=" 1.6; color: #8e8e8e; font-family: Arial, Tahoma, Helvetica, FreeSans, sans-serif; font-size: 13.5px; background-color: #ffffff;"><div></div></div><div id="post-body-6094840464080840069" itemprop="description articleBody" style="font-size: 14.85px; font-family: Arial, Tahoma, Helvetica, FreeSans, sans-serif; background-color: #ffffff;"><div dir="ltr" trbidi="on">&nbsp;How to achieve&nbsp;below code in calculated column?</div><div><br />if(Month = "Jan")<br />then MonInNum = 1<br />else if(Month = "Feb")<br />then <span style="font-size: 14.85px;">MonInNum </span>= 2<br />else if(Month == "Mar")<br />then <span style="font-size: 14.85px;">MonInNum </span>= 3</div><div>&nbsp;..................... up to December</div><div>&nbsp;</div></div>