public class Solution {
    public static String getPartOfString(String string) throws TooShortStringException {
        int first = 0;
        int last = 0;
        int countTab = 0;
        String str = null;


        if (string == null) throw new TooShortStringException();
        char[] charsArray = string.toCharArray();

        for (char ch : charsArray) {
            if (ch == '\t') countTab++;
        }

        if (countTab < 2) throw new TooShortStringException();
        else {
            countTab = 0;
            for (int i = 0; i < charsArray.length; i++) {
                if (charsArray[i] == '\t') {
                    countTab++;
                    first = i + 1;
                }
                break;
            }

            countTab = 0;
            for (int i = 0; i < charsArray.length; i++) {
                if (charsArray[i] == '\t') {
                    countTab++;
                    if (countTab == 2) {
                        last = i;
                    }
                }
            }

            str = string.substring(first, last);
        }

        return  str ;
    }

    public static class TooShortStringException extends Exception {
    }

    public static void main(String[] args) throws TooShortStringException {
        System.out.println(getPartOfString("\t\tJavaRush - лучший сервис обучения Java."));
    }
}