No such element found exception in java

i can get correct answers in custom input but when i submit it shows wrong answers and if i run without custom input , it shows the above error
/* package codechef; // don’t place package name! */

import java.util.;
import java.lang.
;
import java.io.*;

/* Name of the class has to be “Main” only if the class is public. */
class Codechef
{
static Scanner scn = new Scanner(System.in);
public static void main (String[] args) throws java.lang.Exception
{
// your code goes here
String s = scn.next();
System.out.println( sub_pall(s));
}

public static int sub_pall(String args)
{
    
    int len = args.length();
    int ans = 0;
    for(int i=1;i<2*(len);i++)
    {
        int l_idx = ((i-1)/2)-1;
        int u_idx = ((i-1)/2)+1;
        int nos = 1;
        if(i%2==0)
        {
          
            nos = 0;
            l_idx = ((i-1)-1)/2;
            u_idx = ((i+1)-1)/2;
            
        }
        if(i%2!=0)
        {
            int r = Integer.parseInt(args.substring((i-1)/2,((i-1)/2)+1));
            if(r%3!=0)
            {
                continue;
            }
        }
      while(l_idx>=0 && u_idx<len)
      {
          if(args.charAt(l_idx)==args.charAt(u_idx))
          {
              int x = Integer.parseInt(args.substring(l_idx,u_idx+1));
              if(x%3==0 && args.charAt(l_idx)!='0')
              nos++;
              l_idx--;
              u_idx++;
          }
          else{
              break;
          }
      }
      ans+=nos;
     
    }
    return ans;
}

}