Monistus

#include<bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    
    string m;
    cin >> m;

    stack<char> s;
    for(int i = m.size()-1; i >= 0; i--) s.push(m[i]);

    while(!s.empty()){
        char c = s.top(); s.pop();
        if(isdigit(c)){
            int x = c - '0';

            vector<char> v;
            for(int i = 0; i < x; i++){
                v.push_back(s.top()); s.pop();
            }
            reverse(v.begin(), v.end());

            for(char d : v) s.push(d);
            for(char d : v) s.push(d);            

        }
        else{
            cout << c;
        }
    }



    /* 

    82silisko
    2silisko2silisko
    sisiliskosisilisko

    mis3si1pi
    missi1si1pi
    mississippi

    */
}

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: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED