Adding a space inbetween a user inputed string

I want a user to enter a String and then add a space in between a character at a chosen interval.

example: user enters: hello then asks for a space every 2 letters. output = he_ll_o_

import java.util.Scanner;

public class stackOverflow {


    public static void main(String[] args) {


        System.out.println("enter a string");
        Scanner input = new Scanner(System.in);
        String getInput = input.nextLine();

        System.out.println("how many spaces would you like?");
        Scanner space = new Scanner(System.in);
        int getSpace = space.nextInt();


        String toInput2 = new String();

        for(int i = 0; getInput.length() > i; i++){

        if(getSpace == 0) {
            toInput2 = toInput2 + getInput.charAt(i);
            } 
        else if(i % getSpace == 0) {
            toInput2 = toInput2 + getInput.charAt(i) + "_"; //this line im having trouble with.
            }

        }


        System.out.println(toInput2);

    }



}

Thats my code so far, it might be the completely wrong way of solving it, so correct me if im wrong. thanks in advance :)