Monistus

#include <iostream>
#include <string>
#include <vector>
#include <cctype>
using namespace std;

// other version
int main() {
    string s, t;
    cin >> s;

    vector<string> res;
    unsigned long long i = 0;

    while (i < s.size()) {
        if (isdigit(s[i])) {
            int length = s[i] - '0'; 
            t = s.substr(i + 1, length);
            res.push_back(s.substr(0, i));
            s = t + s.substr(i + 1);
            i = 0;
        } else {
            i++;
        }
    }

    for (const string& part : res) {
        cout << part;
    }
    cout << s << 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: 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