Convert Java to Dex

I added the following code to my game and now it is unable to convert thwe game to APK because of unable to convert java to DEX. here is the new code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Advertisements;

public class ads : MonoBehaviour
{
private string store_id = "3135934";
private string video_ad = "video";
private string banner_ad = "banner";

void Start()
{
Advertisement.Initialize(store_id,false);
request_banner();
}

public void request_ad()
{
if (Advertisement.IsReady(video_ad))
{
Advertisement.Show();
}
}

void request_banner()
{
if (Advertisement.IsReady(banner_ad))
{
Advertisement.Show();
}
}
}

 

USE CODE TAGS:
https://forum.unity.com/threads/using-code-tags-properly.143875/