Language: C++

#include <iostream>
#include <string>
#include <map>

using namespace std;

void C_121()
{
	int N, M;
	cin >> N >> M;

	map<int, int> drink;
	for (int i = 0; i < N; ++i)
	{
		int A, B;
		cin >> A >> B;

		if (drink.count(A) == 0) drink[A] += B;
    else drink.insert(A, B);
	}

  int cost_sum = 0;
  for (auto itr = drink.begin(); itr != drink.end(); ++itr)
  {
    int cost = itr->first;
    int stock = itr->second;

    if (M <= stock)
    {
      cost_sum += cost * M;
      break;
    }
    else
    {
      M -= stock;
      cost_sum += cost * stock;
    }
  }
  cout << cost_sum << endl;
}

int main()
{
	//C_120();
  C_121();
}

Compiler output:
In file included from /usr/include/c++/14/map:63,
                 from a.cc:3:
/usr/include/c++/14/bits/stl_map.h: In instantiation of 'void std::map<_Key, _Tp, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >]':
a.cc:19:22:   required from here
   19 |     else drink.insert(A, B);
      |          ~~~~~~~~~~~~^~~~~~
/usr/include/c++/14/bits/stl_map.h:943:38: error: no matching function for call to 'std::_Rb_tree<int, std::pair<const int, int>, std::_Select1st<std::pair<const int, int> >, std::less<int>, std::allocator<std::pair<const int, int> > >::_M_insert_range_unique(int&, int&)'
  943 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/map:62:
/usr/include/c++/14/bits/stl_tree.h:1096:9: note: candidate: 'template<class _InputIterator> std::__enable_if_t<((bool)std::is_same<_Val, typename std::iterator_traits<_InputIterator>::value_type>::value)> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_range_unique(_InputIterator, _InputIterator) [with _Key = int; _Val = std::pair<const int, int>; _KeyOfValue = std::_Select1st<std::pair<const int, int> >; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >]'
 1096 |         _M_insert_range_unique(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:1096:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_tree.h: In substitution of 'template<class _InputIterator> std::__enable_if_t<((bool)std::is_same<std::pair<const int, int>, typename std::iterator_traits< <template-parameter-1-1> >::value_type>::value), void> std::_Rb_tree<int, std::pair<const int, int>, std::_Select1st<std::pair<const int, int> >, std::less<int>, std::allocator<std::pair<const int, int> > >::_M_insert_range_unique(_InputIterator, _InputIterator) [with _InputIterator = int]':
/usr/include/c++/14/bits/stl_map.h:943:31:   required from 'void std::map<_Key, _Tp, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >]'
  943 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
a.cc:19:22:   required from here
   19 |     else drink.insert(A, B);
      |          ~~~~~~~~~~~~^~~~~~
/usr/include/c++/14/bits/stl_tree.h:1095:58: error: no type named 'value_type' in 'struct std::iterator_traits<int>'
 1095 |         __enable_if_t<__same_value_type<_InputIterator>::value>
      |                                                          ^~~~~
/usr/include/c++/14/bits/stl_map.h: In instantiation of 'void std::map<_Key, _Tp, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >]':
a.cc:19:22:   required from here
   19 |     else drink.insert(A, B);
      |          ~~~~~~~~~~~~^~~~~~
/usr/include/c++/14/bits/stl_tree.h:1105:9: note: candidate: 'template<class _InputIterator> std::__enable_if_t<((bool)(! std::is_same<_Val, typename std::iterator_traits<_InputIterator>::value_type>::value))> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_range_unique(_InputIterator, _InputIterator) [with _Key = int; _Val = std::pair<const int, int>; _KeyOfValue = std::_Select1st<std::pair<const int, int> >; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >]'
 1105 |         _M_insert_range_unique(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:1105:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_tree.h: In substitution of 'template<class _InputIterator> std::__enable_if_t<((bool)(! std::is_same<std::pair<const int, int>, typename std::iterator_traits< <template-parameter-1-1> >::value_type>::value)), void> std::_Rb_tree<int, std::pair<const int, int>, std::_Select1st<std::pair<const int, int> >, std::less<int>, std::allocator<std::pair<const int, int> > >::_M_insert_range_unique(_InputIterator, _InputIterator) [with _InputIterator = int]':
/usr/include/c++/14/bits/stl_map.h:943:31:   required from 'void std::map<_Key, _Tp, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = int; _Key = int; _Tp = int; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, int> >]'
  943 |         { _M_t._M_insert_range_unique(__first, __last); }
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
a.cc:19:22:   required from here
   19 |     else drink.insert(A, B);
      |          ~~~~~~~~~~~~^~~~~~
/usr/include/c++/14/bits/stl_tree.h:1104:59: error: no type named 'value_type' in 'struct std::iterator_traits<int>'
 1104 |         __enable_if_t<!__same_value_type<_InputIterator>::value>
      |                                                           ^~~~~