Monistus

#include <iostream>
#include <string>

using namespace std;

int main()
{
    string input;
    cin >> input;

    size_t digitPos;
    while ((digitPos = input.find_first_of("123456789")) != string::npos)
    {
        int digit = input[digitPos] - '0';
        string substring = input.substr(digitPos + 1, digit);

        // Duplicate the substring on the right side of the digit
        input.insert(digitPos + 1, substring);

        // Remove the digit
        input.erase(digitPos, 1);
    }

    cout << input << endl;

    return 0;
}

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: TIME LIMIT EXCEEDED

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