Monistus

#include <iostream>
#include <string>

std::string solve(const std::string& string) {
    std::string solved_string;
    char c;
    int  v;
    for (size_t i=0; i < string.length(); i++) {
        c = string[i];
        v = string[i] - '0';
        if (0 < v && v < 10) { 
            solved_string += solve(string.substr(i+1, v)); 
            continue;
        }
        solved_string += c;
    }
    return solved_string;
}


int main()
{
    std::string string;
    std::cin >> string;
    string = solve(string);
    std::cout << string << '\n';
    return 0;
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 1, 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: WRONG ANSWER

Test 4

Group: 1, 2

Verdict: ACCEPTED

Test 5

Group: 1, 2

Verdict: WRONG ANSWER

Test 6

Group: 1, 2

Verdict: WRONG ANSWER

Test 7

Group: 1, 2

Verdict: WRONG ANSWER

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: WRONG ANSWER

Test 10

Group: 2

Verdict: WRONG ANSWER

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED