function solve() {

   let prices = {
      "js-fundamentals" : 170,
      "js-advanced" : 180,
      "js-applications" : 190,
      "js-web" : 490,
   }
   let names = {
      "js-fundamentals" : "JS-Fundamentals",
      "js-advanced" : "JS-Advanced",
      "js-applications" : "JS-Applications",
      "js-web" : "JS-Web",
      "HTML and CSS" : "HTML and CSS",
   }


   document.getElementsByTagName("button")[0]
      .addEventListener("click", (e)=>{
      let selectedCourses = [...document.querySelectorAll("[type=checkbox]")]
      .filter(x=>x.checked===true)
      .map(x=>x.value);

      if (selectedCourses.includes("js-advanced")
      && selectedCourses.includes("js-fundamentals")) {
         prices["js-advanced"] = 0.9*prices["js-advanced"];
      }

      let total = selectedCourses
                  .reduce((price,curr)=>price+prices[curr],0);

      if (selectedCourses.includes("js-advanced")
      && selectedCourses.includes("js-fundamentals")
      && selectedCourses.includes("js-applications")) {
         total = 0.94*total;
      }

      if (selectedCourses.includes("js-advanced")
       && selectedCourses.includes("js-fundamentals")
       && selectedCourses.includes("js-applications")
       && selectedCourses.includes("js-web")) {
         selectedCourses.push("HTML and CSS");
      }

      let onlineCourse = document.querySelectorAll("input[type=radio]")[1];
      if (onlineCourse.checked === true) {
         total = 0.94*total;
      }

      let cost = document.getElementsByClassName("courseFoot")[1].getElementsByTagName("p")[0];
      cost.innerText = `Cost: ${Math.floor(total).toFixed(2)} BGN`;

      document.getElementById("myCourses").childNodes;

      const ul = document.getElementsByClassName("courseBody")[1].getElementsByTagName("ul")[0];
      selectedCourses
      .forEach(e=>{
      const li = document.createElement("li");
      li.innerText = names[e];
      ul.appendChild(li);
      });
   });
}

solve();