Splitting strings Java code coach

Question

Only 2 hidden test cases fail and i don’t know why. Here’s my code:
import java.util.*;
public class Program
{
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
String s = input.nextLine();
int n = input.nextInt();
ArrayList<Character> r = new ArrayList<Character>();
String res = "";
for(int i=0;i<s.length();i++){
if(i==n){
n=n+n;
r.add('-');
}
r.add(s.charAt(i));

}
for(char j : r){
res += j;
}
System.out.println(res);
}
}

Answer 1

Nikola Markov , your code could be rewritten this way. Add the symbol "-", only if position in string is multiple of n and differ from 0. Look at the code. Hope it helps you.
https://code.sololearn.com/c2R13bRmJ47R/?ref=app

Answer 2

Thank you for the help!