Guys, i run program and it works. Why does it crash?
Could you point me to the problem in my code?

public static void main(String[] args) throws IOException {
        int sum=0;
        Scanner s = new Scanner (System.in);
        int a = s.nextInt ();

        BufferedReader br = new BufferedReader (new InputStreamReader (System.in));
        String s1 = br.readLine ();


        for (int i = 0; i<a-2; i++) {
            if (s1.charAt (i)==s1.charAt (i+1) && s1.charAt (i) == s1.charAt (i+2)) {
            String s2 = Character.toString (s1.charAt (i));
            sum = Integer.parseInt (s2);
            System.out.print (sum*3 + " ");

            }
        }

        for (int i = 0; i<a-2; i++) {
            if (s1.charAt (i)==s1.charAt (i+1) && s1.charAt (i) == s1.charAt (i+2)) {

                System.out.print (s1.indexOf(s1.charAt (i))+2);

            }