<input type="text" name="verify" id="verify" required class="contact-input">

var rnuma = Math.floor(Math.random() * 5);
var rnumb = Math.floor(Math.random() * 5);
var sum = rnuma + rnumb;

$("#contact-form").validate({
    rules: {
         verify: {
              value: sum
         },
    },
});