I'm getting NZEC error on the video game problem(ZCO 2014-Contest Page ).

How do i prevent this from happening again?I read a quora answer(https://www.quora.com/What-are-the-various-reasons-that-can-cause-NZEC-errors-on-online-coding-platforms) which was suggested to some other user who had the same problem,I didn't understand a single bit of it,can someone help me figure out the runtime error(NZEC) in the above program and how to i prevent it from happening in the future?

Code:

import java.util.*;
public class videogame{
    public static  void main(String args[]){
        Scanner in = new Scanner(System.in);
        int n,h,j,x;
        int i;
        n=in.nextInt();
        h=in.nextInt();
        int heights[] = new int[n];
        for(i=0;i<n;i++){< pre="">
            j=in.nextInt();
            if(j<=h) {
                heights[i] = j;
            }
            else{
                heights[i]=0;
            }
        }
        int z=0;
        boolean k = false;
        while(true){
            x=in.nextInt();
            if(x==1){
                if(z>0){
                    z--;
                }
                else{
                    z=0;
                }
            }
            else if(x==2){
                if(z<n){< pre="">
                    z++;
                }
                else{
                    z=n-1;
                }
            }
            else if(x==3&&k==false){
                if(heights[z]>0) {
                    heights[z]--;
                    k=true;
                }
            }
            else if(x==4&&k==true){
                if(heights[z]<h){< pre="">
                    heights[z]++;
                    k=false;
                }
            }
            else if(x==0){
                break;
            }
            else{
                continue;
            }
        }
        for(i=0;i<n;i++){< pre="">
            System.out.print(heights[i]+" ");
        }
    }
}