How to remove left and right margin on first and last div

I have more than 100 divs on the page and each row has 3 divs. I want to remove left margin from first div and right margin from right div whereas center div should have 15px margin from left and right. Please guide me how can I do that without giving specific classes (no margin) on each div. Here is the example here is my css code ``` .prp_box{ margin:15px 15px; width:100px; height:100px; background:#5f03a6; } ```