Language: C++

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	string s;
	int k;
	cin >> s >> k;

	vector<string> t;
	for (int i = 0; i < s.length(); i++) {
		for (int j = 1; j <= min(7u, s.length() - i); j++) {
			t.emplace_back(s.substr(i, j));
		}
	}

	sort(t.begin(), t.end());
	unique(t.begin(), t.end());

	cout << t[k - 1] << endl;

	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:16:41: error: no matching function for call to 'min(unsigned int, std::__cxx11::basic_string<char>::size_type)'
   16 |                 for (int j = 1; j <= min(7u, s.length() - i); j++) {
      |                                      ~~~^~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:233:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)'
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
a.cc:16:41: note:   deduced conflicting types for parameter 'const _Tp' ('unsigned int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'})
   16 |                 for (int j = 1; j <= min(7u, s.length() - i); j++) {
      |                                      ~~~^~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)'
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:4:
/usr/include/c++/14/bits/stl_algo.h:5686:5: note: candidate: 'template<class _Tp> constexpr _Tp std::min(initializer_list<_Tp>)'
 5686 |     min(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5686:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5696:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::min(initializer_list<_Tp>, _Compare)'
 5696 |     min(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5696:5: note:   template argument deduction/substitution failed:
a.cc:16:41: note:   mismatched types 'std::initializer_list<_Tp>' and 'unsigned int'
   16 |                 for (int j = 1; j <= min(7u, s.length() - i); j++) {
      |                                      ~~~^~~~~~~~~~~~~~~~~~~~
a.cc:22:15: warning: ignoring return value of '_FIter std::unique(_FIter, _FIter) [with _FIter = __gnu_cxx::__normal_iterator<__cxx11::basic_string<char>*, vector<__cxx11::basic_string<char> > >]', declared with attribute 'nodiscard' [-Wunused-result]
   22 |         unique(t.begin(), t.end());
      |         ~~~~~~^~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algo.h:891:5: note: declared here
  891 |     unique(_ForwardIterator __first, _ForwardIterator __last)
      |     ^~~~~~