Monistus

import java.util.HashSet;
import java.util.Scanner; 
 
 
public class Monistus {
    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in); 
        String str = sc.nextLine(); 
        sc.close(); 
 
        StringBuilder mjono = new StringBuilder();
        mjono.append(str);
 
        HashSet<Character> numerot2 = new HashSet<Character>();
 
        numerot2.add('1');
        numerot2.add('2');
        numerot2.add('3');
        numerot2.add('4');
        numerot2.add('5');
        numerot2.add('6');
        numerot2.add('7');
        numerot2.add('8');
        numerot2.add('9');
        int numero = 0; 
 
 
        for(int i = 0; i < mjono.length(); i++){
            if (numerot2.contains(mjono.charAt(i))) {
                char charNumero = mjono.charAt(i); 
                numero = Character.getNumericValue(charNumero); 
                String aliJono = mjono.substring(i + 1, i + numero + 1);
                mjono.deleteCharAt(i); 
                mjono.insert(i, aliJono);  
                i = i - 1; 
            } 
 
 
        }
 
        System.out.println(mjono);
 
    }
 
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 1, 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: ACCEPTED

Test 4

Group: 1, 2

Verdict: ACCEPTED

Test 5

Group: 1, 2

Verdict: ACCEPTED

Test 6

Group: 1, 2

Verdict: ACCEPTED

Test 7

Group: 1, 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 10

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 11

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 12

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 13

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 14

Group: 2

Verdict: TIME LIMIT EXCEEDED