func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     string s;     cin >> s;     multiset<char> ms;     for (char c : s) ms.insert(c);     string t, u;     for (int i = 0; i < (s.size()); i++) {       ms.erase(ms.find(s[i]));       t += s[i];       while (!t.empty() && ms.lower_bound(t.back()) == ms.begin()) {         u += t.back();         t.pop_back();       }     }     cout << u << endl;   }   